Why Chemistry



Why Chemistry?

CHEMISTRY is the study of _______________________________________________

Like all scientists, chemists try to describe and explain the world.

Chemists start by asking questions. To answer these questions, chemists develop

Long before science, humans invented chemical techniques and processes. This included

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Describing Matter

Recall that MATTER is _________________________________________________

Being able to describe matter is an important skill.

Characteristics used to describe matter are called PROPERTIES.

Some properties include:

A PHYSICAL PROPERTY is a property that _______________________________________________________________________. (ex. Anthocyanins can be blue in colour)

A CHEMICAL PROPERTY ________________________________________________________________________. (ex. Glucose can be combined with Oxygen to produce Carbon Dioxide and Water)

Some properties are qualitative (describe with words) and some are quantitative (can be measured)

Measurement

In science we use Le Système international d’unités, or SI units. SI units are based on the metric system.

In the metric system all units are multiples of 10.

The metric system uses base units. Examples are the metre (m), cubic metre (m3), kilogram (Kg), second (s), degree Kelvin (K), mole (mol) and the joule (J).

|Prefix |Symbol |Relationship to base unit |

|giga- | | |

| | | |

|kilo- |k | |

| | | |

| | | |

|-------------base------------- |------------------------------- |10o = 1 |

| | | |

|centi- |c | |

|milli- |m | |

| | | |

| | | |

35 cm = __________ m

20 s = ________ ms

450 um = _________ cm

0.034 kl = _________ ml

8000 dJ = _________ MJ

1750 cm3 = _________ m3

In science we express #’s in SCIENTIFIC NOTATION

In scientific notation we write #’s in the form: Z x 10n

Z is always a number greater than 1 and less than 10.

1. Write the number 58000000 in scientific notation.

2. Write the number 0.000000024 in scientific notation.

Practice: Write in Scientific Notation

A. 3400000000 B. 0.00234

Physical Measurements

Numbers you can count or numbers that are true by definition are called EXACT NUMBERS.

Ex.

When we use equipment to measure matter, we must have a way to record how exact are measurements will be.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

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Ruler A Ruler B

Ruler B is more precise than Ruler A

The digits that you record when you measure something are called _________________________ ________________________________

Rules for Determining Significant Digits

1. All non-zero numbers are significant.

2. All zeros that are located between two non-zero numbers are significant.

3. Zeros that are located to the left of a value are not significant.

4. Zeros that are located to the right of a value may or may not be significant.

a. This is where scientific notation becomes important

Rules for Reporting Significant Digits in Calculations

When doing calculations, you must keep the correct # of significant digits, so that your results do not imply more certainty than your measured quantities justify.

Rule 1: Multiplying and Dividing

The value with the fewest number of significant digits, determines the number of significant digits in your answer.

Rule 2: Adding and Subtracting

The value with the fewest number of decimal places determines the number of decimal places in your answer.

Rule 3: Rounding

If your answer ends in a number that is greater than 5, increase the preceding digit by 1.

If your answer ends with a number that is less than 5, leave the preceding number unchanged.

If your answer ends with 5, increase the preceding number by 1 if it is odd, leave the preceding number unchanged if it is even.

Ex 1.

A student measures a brick of silver and found it to be 6.78cm long, 0.98cm wide and 11.46cm high. Determine the volume of the brick.

Ex 2. You measure the mass of 4 objects, 11.4g, 134.56g, 45.0g, and 98.435g. What is the total mass of the objects?

The Atom

Recall:

|Subatomic Particle |Charge |Symbol |Mass |Atomic Mass Unit |

| | | | | |

| | | | | |

| | | | | |

If you could put 6.02 x 1023 p+ and no on a scale they would have a mass of about 1g.

Therefore:

This makes it inconvenient to measure in grams so chemists use the ATOMIC MASS UNIT (u)

Modern Atomic Theory

1. All matter is made of __________________________________________________________________

2. Atoms of 1 element __________________________________________________________________

3. Atoms of 1 element __________________________________________________________________

4. Atoms combine in __________________________________________________________________

5.

Recall: Standard Atomic Notation

X = =

A = =

Z = =

How do you infer the number of electrons?

ISOTOPES

All neutral atoms of the same element contain ________________________________________________________________________

The number of neutrons can vary.

Example:

_______________________________________________________________________

________________________________________________________________________

These 3 forms are called _____________________________.

Isotopes ________________________________________________________________

All the isotopes have similar chemical properties, but some of them are UNSTABLE than others.

Unstable means that their nuclei are more likely to DECAY or come apart releasing energy and subatomic particles.

This is called ________________________ and the atoms are called _______________.

Atomic Mass and Isotopes

Refer to Chapter 5 for information below

Atomic mass units are a ____________________________________________________

________________________________________________________________________________________________________________________________________________

The mass of all other atoms are measured relative to carbon-12

Most elements are made up of 2 or more isotopes.

Because isotopes have different #s of neutrons, _________________________________. This must be accounted for when ____________________________________________.

For example Mg has 3 naturally occurring isotopes.

___________________________________________________________________________________________________________.

These isotopes are present in different amounts.

In nature _______________________________________________________________.

The relative amount of each isotope is called the ________________________________.

To determine the mass of a Mg atom the isotopic abundance must be accounted for.

AVERAGE ATOMIC MASS

The _____________________________________________ of an element is the _______________________________________________________________________.

The mass given for each element on the periodic table ___________________________.

To determine the _____________________________________________, chemists use a device called a ___________________________________________________________

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Once the data is obtained the ______________________________________ can be calculated by finding the ____________________________________.

|Isotope |Isotopic Abundance |Mass (u) |

| | |23.985041700 |

| | |24.98583692 |

| | |25.982592929 |

For Mg:

Average Atomic Mass

=

=

=

|Isotope |Isotopic Abundance |Mass (u) |

|35Cl |75.78% |34.96885268 |

|37Cl |24.22% |36.96590259 |

You try chlorine:

If you know the average atomic mass of an element and the masses of its isotopes you can ____________________________________________________________________.

Example:

Boron exists as two naturally occurring isotopes: 10B (10.01u) and 11B (11.01u). Boron has an average atomic mass of 10.81u. Calculate the isotopic abundance of each isotope.

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Electrons occupy space around the nucleus.

They are the first subatomic particle to interact when atoms get close together.

The # of e- and their arrangement will determine how a particular atom reacts.

Electrons are restricted to fixed regions around the nucleus.

These are volumes of space where the e- can be.

You probably called these orbits (Bohr – Rutherford)

We are now going to call them ENERGY LEVELS.

e- close to the nucleus have ____________________ so they are in a ______________.

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How is this bookshelf the same?

Recall: There is a certain # of electrons that each energy level can hold.

The energy levels in atoms and the arrangement of electrons is very closely related to the

structure of the ___________________________________________________.

The Periodic Table

__________________ _________________________ (1834–1907) sequenced the known elements (65) in order of increasing atomic mass. The result was a table of the elements, organized so that elements with similar properties were arranged in the same column. This organization resulting in periodic (repeating) of patterns and was called the

________________________________________________________________________

The modern periodic table is arranged by atomic number and the ___________ _______:

________________________________________________________________________

________________________________________________________________________

The ____________ ____________ (repeating patterns) that result from organizing the elements by their atomic number are linked to the way in which electrons occupy and fill energy levels.

Remember Bohr-Rutherford Diagrams?

There are a couple of important patterns that emerge when you draw Bohr-Rutherford diagrams of the elements.

1. _________________________________________________________________

____________________________________________________________________

2. __________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

There is a more convenient way to represent atoms than B/R diagrams. _____________ ___________________ (grade 10) use the atomic symbol and show only the valence electrons to represent an atom.

Stable Atoms

Group 18 (VIII A) are the only elements that exist as individual atoms in nature. They are very _________________________. Since chemical reactivity is determined by ________________ _____________________, there must be something about the noble gases electron arrangement that makes them so un-reactive.

All the noble gases have ________________________________________________________________________

What does this stability mean? ________________________________________________________________________.

Scientists have observed that, in nature, situations or systems of lower energy are favoured over situations or systems of higher energy. When atoms have eight electrons in the outer energy level, they have _______________ __________________ _______________, and we say they have a ____________________ _____________________________.

Atoms and the Periodic Table

Chemists define, and measure, an atom’s size in terms of its radius. The radius of an atom is the distance from its nucleus to the approximate outer boundary.

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Atomic Radius

There are two general trends for atomic size:

1. As you go _____________________ in the periodic table, the size of an atom _____________________.

i. The valence electrons occupy an energy level that is ______________________________________________________

ii. Electrons experience ______________________________________________________

iii. Inner energy levels ______________________________________________________

2. As you go _________________________, the size of an atom ________________

i. positive charge on the nucleus also increases across a period. ______________________________________________________

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ii. without additional energy the electrons are restricted to their outer energy level.

Ionization Energy

An Ion is a charged atom.

________________________________________________________________________

________________________________________________________________________

Main group metals tend to _________________________________

Non-metals tend to ___________________________

It takes energy to overcome the attractive force of a nucleus and pull an electron away from a neutral atom. The energy that is required to remove an electron from an atom is called ___________________________ ______________________________.

The ionization energy that is needed to remove one electron from the outer energy level of the atoms of the main-group elements is called the 1st Ionization Energy.

It is measured in units of _____________. A kilojoule (kJ) is a unit of energy. A mole (mol) is an amount of a substance.

Atoms that give up electrons easily have _______________________________________.

There are two general trends for ionization energy.

1. Ionization energy tends to decrease down a group.

i. ____________________________________________________________________________________________________________

2. Ionization energy tends to increase across a period.

i. __________________________________________________________________________________________________________________________________________________________________.

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Electron Affinity

Some atoms have a low attraction for electrons and others a greater attraction.

___________________________ is a measure of the change in energy that occurs when an electron is added to the outer energy level of an atom to form a negative ion.

If energy is released when an atom of an element gains an electron, the electron affinity is expressed as a ________________________________.

When energy is absorbed when an electron is added, electron affinity is low, and is expressed as a ________________________________.

Metals have very __________ electron affinities

Although the trends are not as apparent, in general the trends for electron affinity are:

1. _________________________________________________________________

2. _________________________________________________________________

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Classifying Chemicals

Based on their physical properties, chemicals can be divided into 2 groups:

1.

2.

|Property |Ionic |Covalent |

|State | | |

|Melting Point | | |

|Conductivity as a liquid | | |

|Solubility in Water | | |

|Conducts Electricity in Water | | |

Salt is an ionic compound.

-

-

-

-

Carbon Dioxide is a covalent compound.

-

-

-

-

Chemical Bonding

The differences in properties between ionic and covalent compounds is a result of the interaction between the valence e- of the atoms in each.

When atoms interact either:

1. _______________________________________________________________.

a. This results in an ________________________

2. _______________________________________________________________.

a. This results in a _________________________

When atoms interact, they each attract the other atom’s e-.

________________________________________ is a measure of an atom’s ability to attract electrons in a chemical bond.

By using _________________________ we can determine ________________________________________________________________________

Each element has an ______________________________ value.

Also, _______________________________ of elements shows a periodic trend.

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Predicting Bond Type

To predict bond type we ____________________________________________ between 2 atoms ((EN)

(EN = ________________________________________________

(EN

3.3 1.7 0.5 0

Ex.

Na and Cl

N and N

C and O

Bonding and the Octet Rule

Atoms form bonds to become _____________________________________________.

To become stable atoms want to have ______________________________________. Two atoms that have the same electron arrangement are said to be _______________________________.

Atoms can ______________________________________________ to achieve this.

Ex NaCl

- (EN =

-

-

-

Lewis Structures:

Try Ca and O

Try Mg and Cl

Conductivity of Ionic Compounds

Ionic compounds are not good conductors as a solid.

Ionic compounds are good conductors as liquids.

Ionic compounds are good conductors when dissolved in water.

WHY?

________________________________________________________________________________________________________________________________________________________________________________________________________________________

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________________________________________________________________________________________________________________________________________________________________________________________________________________________

Covalent Bonding

A covalent Bond _________________________________________________________.

Covalent Bonds form when (EN = ___________________

For example think of Chlorine gas Cl2

If the electrons are shared equally (EN = 0.0, then the bond is a _______________________________________________________________________. Atoms that bond this way form _____________________________________________.

What about C and H

(EN =

C and H form a covalent bond as their electron are almost shared equally

Multiple Bonds

Atoms can share 1,2, or 3 pairs of electrons.

Oxygen Gas for example.

What about Nitrogen Gas

Conductivity of Covalent Compounds

Covalent compounds have a wide variety of properties.

Some dissolve in water, some do not.

Some conduct electricity in their liquid form. Some do not.

If we focus on pure covalent compounds like those above, their properties are all similar. All have low boiling points and none conduct electricity. Why?

1. __________________________________________________________________

2. ____________________________________________________________________________________________________________________________________

Covalent compounds (_____________________________________________________) do not form lattice structures like ionic compounds.

The molecules are held together by _______________________________. (more later)

The covalent bonds within a molecule are called ________________________________.

_______________________________________________________________________________________________________________________________________________.

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Metallic Bonding

Non-metals tend to form ____________________________________ with metals.

Non-metals tend to form ____________________________________ with non-metals.

What about metals bonding with metals?

(EN between metal atoms is ________________________________________________.

Evidence proves this. Pure metals like sodium can be cut with a knife, copper can be pulled into wires. ___________________________________________.

Metals ________________________________________________________________ with other metals. Therefore they do not form ________________________________.

Metals _________________________________________________________________.

Think of a swimming pool of people (metal atoms) sharing the water (electrons).

The atoms form _________________________________________.

The electrons _______________________________________________________. What happens when you hammer metal. ______________________________________.

Polar Covalent Bonds

When (EN is between 0.5 and 1.7 we get a special kind of covalent bond called a ______________________________

This difference is significant. Not enough ____________________________________________________________, but significant enough that the bonding pair of electrons ____________________________________________________________ atoms.

The best example of this is in a __________________________________.

The (EN between H and O is ______________________________.

This results in a _________________________________________.

This means that the bonding electron pair spends more time ______________________________________________________________________.

Because of this the oxygen atom ________________________________________ compared to the hydrogen atom, which will be _______________________________________________________ than the oxygen.

We say the oxygen has a _________________________________________________ and the hydrogen has a __________________________________________________.

It looks like this

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If we look at a complete water molecule and the bonds within it we see:

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Molecular Shapes

Different molecules form _____________________________________.

Shape is based on __________________________________.

By drawing __________________________, you can determine the shape of molecules.

Ex. Draw the Lewis structure for water.

Water is surrounded by ____________________________________________.

2 pairs are involved in bonding, 2 pairs are not.

If involved with bonding pairs are called: _______________________________

If not involved in bonding pairs are called: ______________________________

Electron pairs are arranged so that ____________________________________________________ (________________)

So in water:

Ex. 2 Carbon Dioxide

Ex. 3 Methane

Ex. 4 Ammonia

Polar and Non-Polar Molecules

Lets look at a water molecule again.

The polar bonds in a water molecule along with its shape give water molecules a special property.

They are POLAR MOLECULES

Polar molecules appear to ________________________________________________________________________________________________________________________________________________. Polar Molecules can be called “________________” because of their –ve and +ve poles.

In the case of water, this polarity causes _______________________________________.

This also accounts for waters _______________________________________________.

Some molecules are ___________________________________________.

This means that they do not ________________________________________________.

For example CO2

- The bonds in CO2 are ___________________, but this does not mean the molecule is _____________________________.

- CO2 is a _______________________ which causes it to not to have +ve and –ve poles.

Non-polar molecules tend to have ________________________________________________________________________________________________________________________________________________

Writing Chemical Formulas and Naming Chemical Compounds

Chemical Formula – ________________________________________________________________________________________________________________________________________________

When writing chemical formulas:

1. The less electronegative element or ion is _________________.

2. The final formula _______________________________ (MgO)

3. The number of valance e- needed or lost to achieve a stable octet is called the _________________________________________________________________

a. Group 1 elements have a valence of +1

b. The 1 indicates ______________________________________________.

c. The + indicates ______________________________________________

4. Treat ______________________________ (ions made from more than one atom) as a single ion. You must know the following polyatomic ions and their charges.

|Polyatomic Ion |Formula |Valence |

| | | |

| | | |

| | | |

| | | |

| | | |

See your text for the mnemonic;

____________________________________________________________________.

Zero Sum Rule

__________________________________________________________________________________________________________________________________________

Ex Li and Cl

Ca and F

Mg and O

K and PO4

Sr and CO3

Naming Chemical Compounds

Chemical Nomenclature is the system used in chemistry to name compounds.

The earliest naming was done by naming compounds after places or people

Now the _____________________________________________________________________ (IUPAC) has set international standards for nomenclature.

Binary Compounds

- an inorganic compound containing _____________________________

- Usually __________________________________

- Often ___________________________________

- Less _________________________________________________________

- More ________________________________________________________

- Some transition metals have more than 1 possible valance. The name of the compound must indicate the ion present in the compound by using _____________________________________________________________. This is known as the ____________________________________________.

- The _____________________________________________ uses different endings on the name of the metal to indicate the ion present in the compound.

o ________________ is used to indicate the ______________ valence

o ________________ is used to indicate the ______________ valence

o Does not work well for metals ______________________________

|Element |Root Name |Valence |

| | | +3 +2 |

| | |+2 +1 |

| | |+2 +4 |

| | |+4 +2 |

| | |+2 +1 |

Name and write the formula for

a) Ba and S b)Be and Br c)Fe and P

Naming Compounds with Polyatomic Ions

Same rules as binary compounds apply.

The ending of a polyatomic ion is ________________________________________.

However there are many different polyatomic ions that exist and they have different endings.

|Polyatomic Ion |Formula |Polyatomic Ion |Formula |

| |NO | |PO2 |

| |NO2 | |PO3 |

| |NO3 | |PO4 |

| |NO4 | |PO5 |

|Prefix and Suffix |Number of Oxygen Atoms |

|Hypo__ ______ite | |

|_____________ite | |

|_____________ate | |

|Per__________ate | |

The prefix “thio” means _____________________________________________________________________

Binary Compounds with 2 Non-metals

To name these a ______________________________________________________.

The prefix indicates the _________________________________________________.

The stock system may also be used.

If there is only 1 atom of the first element mono is excluded.

# |1 |2 |3 |4 |5 |6 |7 |8 |9 |10 | |Prefix | | | | | | | | | | | |

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DO INVESTIGATION 1-A pg. 13 NOW

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