CH 5 The Periodic Table - Physical Science 9



CH 5 The Periodic Table

CH 5.1 Organizing the Elements

***Stars produce energy from nuclear reactions. This process has led to the formation of all elements beyond hydrogen and helium.***

Chemical symbol-An abbreviated way to write the name of an element, which consists of one capital letter or one capital and one-two lower case letters. {Examples: carbon (C), chlorine (Cl) and ununtrium (Uut).}

1750’s – Scientists had only identified 17 elements. Mainly metals like iron and copper.

1789–A French chemist Antoine Lavoisier grouped the known elements into categories.

1) Metals 2) Nonmetals 3) Gases 4) Earths

Mendeleev’s Periodic Table

1860’s-Mendeleev was the first scientist to offer the best explanation for how the properties of an element were related to its location in his table. (Based on mass and how they reacted with O and H.)

Proved useful by the discovery of elements with predicted properties that fit into the table.

Modern periodic table- A table of the elements arranged according to repeated changes in properties and the atomic numbers of the elements.

CH 5.2 Modern Periodic Table

The Periodic Law

Periods- The horizontal rows in the periodic table. The atomic number increases as you go across a period from left to right.

Group (or families)- A vertical column in the periodic table. The groups are numbered 1-18. The elements in a group have similar electron configurations and chemical properties.

Classes of Elements

1) Elements are divided into solids, liquids or gases based on their states at room temp.

2) Elements are divided into those that occur naturally and those that do not.

[All but 2 elements with atomic numbers 1 through 92 occur on Earth. Atomic numbers of 93 and higher are synthetic and do not occur naturally.]

3) Elements are put into categories based on their general properties. (Metals, nonmetals and metalloids)

Metals- {Examples: Iron, aluminum, calcium, zinc, sodium, lithium and copper.}

▪ The majority of elements on the periodic table are classified as metals.

▪ Good conductors of electricity and heat.

▪ Except for mercury, metals are solids at room temperature.

▪ Most are malleable.

▪ Many are ductile – they can be drawn into thin wires.

▪ Some are extremely reactive and some do not react easily.

▪ Groups 3-12 are called transition metals.

Transition Metals – Elements that have the ability to form compounds with distinctive colors.

Lanthanide and actinide series elements: These transition elements have more properties in common than elements in other groups.

Nonmetals- {Examples: Oxygen, nitrogen, chlorine, neon, iodine and carbon.}

▪ Generally have properties opposite to those of metals.

▪ Poor conductors of heat and electricity.

▪ Because of low boiling points, many are gases at room temperature.

▪ Nonmetals that are solids at room temperature tend to be brittle.

▪ Some are extremely reactive, some hardly react at all, and some react somewhere in between. {Example: Fluorine in group 17 is the most reactive.}

Metalloids- Have both properties of metals and nonmetals. {Examples: Boron and silicon.}

▪ The ability to conduct electric current varies with temperature.

▪ Pure silicon and germanium are good insulators at low temperatures and good conductors at high temperatures.

Variation Across a Period

The properties within a period change in a similar way from left to right across the table except for Period 1.

Across a period from left to right, the elements become less metallic and more nonmetallic in their properties.

▪ The most reactive metals are on the left side of the table. {Example: Sodium}

▪ The most reactive nonmetals are on the right in group 17.

o Silicon is the least reactive element in period 3 except for argon.

o Chlorine reacts with sulfur and phosphorus and is a highly reactive nonmetal.

o Argon hardly reacts at all.

CH 5.3 Representative Groups

Valence Electrons

A valence electron is an electron that is in the highest occupied energy level of an atom.

▪ Valence electrons play a key role in chemical reactions.

▪ Properties vary across a period because the number of valence electrons increases from left to right.

▪ Elements in a group have similar properties because they have the same number of valence electrons.

Radioactive Elements- Usually lowest in group. Emits charged particles from unstable nuclei. Atoms of one element change into a different element. {Example: uranium-238 decays into thorium-234.}

Radioactive isotopes- Elements that give off radiation as they decay at constant rate.

Half-life- The time it takes of one half of a sample of a radioisotope to decay.

Used for medical purposes and for dating objects.

The Alkali Metals – Li, Na, K, Rb, Cs, Fr

▪ Elements in Group 1

▪ One valence electron

▪ Extremely reactive – found in nature only in compounds (table salt- NaCl)

▪ The reactivity of alkali metals increases from the top of Group 1 to the bottom

The Alkaline Earth Metals – Be, Mg, Ca, Sr, Ba, Ra

▪ Elements in Group 2

▪ Two valence electrons

▪ Harder metals than Group 1

▪ Differences in reactivity are shown by the ways they react with water

▪ Magnesium plays a key role in photosynthesis and building materials

▪ Calcium is needed to keep your bones and teeth strong and is in limestone

Groups 3-12 are Transition Elements with variable

oxidation numbers.

The Boron Family – B, Al, Ga, In, Tl

▪ Elements in Group 13

▪ Three valence electrons

▪ Aluminum is the most abundant metal in Earth’s crust

The Carbon Family – C, Si, Ge, Sn, Pb

▪ Elements in Group 14

▪ Four valence electrons

▪ The metallic nature of the elements increases from top to bottom

▪ Germanium is a better conductor of electric current than silicon

▪ Except for water, most of the compounds in your body contain carbon

▪ Silicon is the second most abundant element in Earth’s crust

The Nitrogen Family – N, P, As, Sb, Bi

▪ Elements in Group 15

▪ Five valence electrons

▪ Nitrogen and phosphorus are the most important elements in Group 15

▪ Besides nitrogen, fertilizers often contain phosphorus

The Oxygen Family – O, S, Se, Te, Po

▪ Elements in Group 16

▪ Six valence electrons

▪ Oxygen is the most abundant element in Earth’s crust

The Halogen Family – F, Cl, Br, I, At

▪ Elements in Group 17

▪ Seven valence electrons

▪ Despite their physical differences, the halogens have similar chem. properties

▪ Highly reactive nonmetals (F is the most reactive)

▪ React easily with most metals to form salts

▪ Colored gases (Cl is green, Br is red-brown, and I is purple)

The Noble Gases – He, Ne, Ar, Kr, Xe, Rn

▪ Elements in Group 18

▪ Helium has two valence electrons (all other elements in Group 18 have 8 valence electrons)

▪ Odorless, colorless and extremely

unreactive

The noble gases emit colors when electricity passes through them.

{Examples: He is pink, Ne is orange-red, Ar is lavender, Kr is white, and Xe is blue.}

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