CHEMISTRY FACTS and FORMULAS TO REMEMBER FOR SOL



CHEMISTRY FACTS and FORMULAS TO REMEMBER for semester 1

Density = Mass/Volume

Precision: How closely experimental values are to each other

Accuracy: How closely experimental values are to the accepted or true value

% Error = Accepted Value - Experimental Value x 100

Accepted Value

Note: % Error is an absolute value and will never be negative

SIGNIFICANT FIGURES:

For numbers that DO NOT contain a decimal place, begin counting from the left at the first non-zero digit and continue counting to the last non-zero digit.

For numbers that DO have a decimal place, begin counting from the left at the first non-zero digit and count all the way to the end of the number.

Addition/Subtraction: Perform calculation and round answer to the least precise value in the calculation (least number of decimal places).

Multiplication/Division: Perform calculation and round answer to the least precise value in the calculation (least number of significant digits).

ATOMIC STRUCTURE:

Atomic Number: Always number of protons in an atom; also, number of electrons in a neutral atom (a neutral atom is one that has neither lost or gained electrons to become an ion).

Atomic Mass: Mass of all protons (1 amu each) and neutrons (1 amu each) in the nucleus of an atom. Note: electrons have a negligible mass and therefore, do not contribute to atomic mass.

Number of Neutrons in an Atom = Atomic Mass – Atomic Number

IONIC COMPOUNDS:

Cation: Metal atom that has lost electrons to become positively charged (remember by the “t” in the middle of the word that looks like a + sign).

Anion: Non-metal atom that has gained electrons to become negatively charged.

Ionization of Atoms:

Group 1 (Alkali Metals): 1+

Group 2 (Alkaline Earth Metals): 2+

Group 13: 3+

Group 14: 4+/4- these do not typically ionize; more involved in covalent bonding

Group 15: 3-

Group 16: 2-

Group 17 (Halogens): 1-

Groups 3-12: 1+/2+/3+ these are the transition metals; you must determine their charge by the ionic formula (the ratio of cations to anions); roman numeral in name refers to cation charge

Ex. FeCl Fe 1+ FeCl2 Fe 2+ FeCl3 Fe 3+

Iron I Chloride Iron II Chloride Iron III Chloride

Polyatomic Ions: An ion made up of 2 or more atoms bonded together that acts as a single unit with a net charge.

Most common polyatomic ions to remember: NH4+ ammonium; OH- hydroxide; NO3- nitrate;

CO32- carbonate; SO42- sulfate; PO43- phosphate

ISOTOPES:

Isotopes: Atoms of the same element with different atomic masses due to differing numbers of neutrons in the nucleus of each.

Ex. C-12 carbon atom with mass of 12 amu 6 protons + 6 neutrons in nucleus

C-13 carbon atom with mass of 13 amu 6 protons + 7 neutrons in nucleus

C-14 carbon atom with mass of 14 amu 6 protons + 8 neutrons in nucleus

Average atomic mass of an atom: weighted average of the naturally occurring isotopes

Avg. Atomic Mass = % abundance (expressed as decimal) x mass of Isotope #1 +

% abundance (expressed as decimal) x mass of Isotope #2 +

% abundance (expressed as decimal) x mass of Isotope #3, etc.

Ex. Chlorine exists naturally as Cl-35 (75% abundance) and Cl-37 (25% abundance)

Avg. Atomic Mass of Chlorine = (0.75)(35 amu) + (0.25)(37 amu) = 35.5 amu

NUCLEAR REACTIONS:

Nuclear Reactions: occurs when nuclei of unstable atoms emit particles and/or rays and often are converted into atoms of another element; associated with the release of high energy/radiation.

Types or Radiation: Alpha 4He particle is released from atom; radiation can be blocked by 2 paper (lowest energy).

Beta 0e a neutron turns into a proton and an electron and the electron

-1 is emitted from the nucleus; radiation is blocked by metal foil.

Gamma 0γ high energy wave is emitted (not a particle); similar to x-rays;

0. almost completely blocked by lead or concrete.

Half life = time it takes for ½ a sample to decay.

% Composition = mass of element x 100

mass of compound

MOLES:

Avogadro’s Number = 6.022 x 1023 particles. Number of particles in 1 mole of any substance

Molar Mass: For atoms, molar mass is the atomic mass expressed in grams.

For compounds, molar mass is the sum of the masses of atoms expressed in grams.

Moles → Particles: (moles)(6.02 x 1023)

Moles → Volume for Gases at STP: (moles gas)(22.4 Liters)

When in doubt, always set up a conversion ratio where the units you desire are on the top and the units you are given (or the units you do not want) are on the bottom.

1 mole of any gas at STP occupies 22.4 Liters

POLARITY:

Bonds between atoms of different electronegativities are always polar; molecules are non-polar if partial charge distribution is symmetrical, polar if charge distribution is asymmetrical.

Difference in polarity greater than 1.7 = Ionic

Difference of less than 0.4 = Non-polar Covalent

Likes Dissolve Likes: Polar solvents dissolve polar/ionic compounds; non-polar dissolve non-polar.

EMPIRICAL/MOLECULAR FORMULAS:

Empirical Formula: Simplest whole number ratio of atoms in a molecule, ex. CH4

Molecular Formula: Actual number of atoms in a molecule, ex. C2H8

Note: Ionic formulas are always empirical

% Composition of each atom in a formula→ Molecular Formula: % to Mass (express % as grams)→ Mass to Moles (mass/molar mass)→Divide by Small (divide each by the smallest no.

of moles) This will give you the ratios of atoms in the molecule.

History of the Atom

[pic]

PERIODIC TRENDS:

[pic]

Across a Period (row): atomic radius decreases, electronegativity and ionization energy increases due to an increased nuclear charge from increased no. of protons in nucleus.

Down a Group (column): atomic radius increases, electronegativity and ionization energy decreases due to the addition of principle energy levels and shielding effect (valence electrons are further removed from nuclear charge and are shielded by inner electrons).

ELECTRONIC CONFIGURATION:

s-sublevel (1 orbital containing up to 2 e-), p-sublevel (3 oribitals each containing up to 2 e-), d-sublevel (5 orbitals each containing up to 2 e-); electrons fill orbitals singularly at 1st

REACTIVITY OF ELEMENTS:

Most reactive metals: Lower left of periodic table (group 1 Alkali metals are most reactive, with Francium being the most reactive).

Most reactive non-metals: Upper right of periodic table (group 17 Halogens are the most reactive, with Flourine being the most reactive).

Note: Group 18 Noble Gases are relatively unreactive since their valence shell already has a full octet of electrons.

TYPES OF CHEMICAL REACTIONS:

Synthesis: A + B → AB (reactants combine to form one product)

Decomposition: AB → A + B (reactants decompose into 2 or more products)

Single Replacement: A + BX → AX + B (occurs when 1 pure metal reacts with an ionic compound and replaces the metal in that compound)

Double Replacement: AX + BY → AY + BX (occurs when 2 ionic compounds react and the metals replace each other)

Combustion: CxHy + O2(g) → CO2(g) + H2O + Energy (occurs when a hydrocarbon is burned in the presence of oxygen)

SHAPES OF MOLECULES:

Linear (SP): Molecule containing 2 atoms or molecule containing 2 atoms on either side of a central atom with no lone pairs of electrons on central atom. Ex. O=C=O CO2

Bent (SP2 or SP3): Molecule containing 2 atoms on either side of a central atom with one or more lone pairs of electrons on the central atom. Ex. H2O

Trigonal Planar (SP2): Usually occurs with molecules containing B or Al as central atom surrounded by three atoms; no lone pairs of electrons are on central atom. Ex. AlCl3

Trigonal Pyramidal (DSP3): Molecule containing one central atom with three surrounding atoms; central atom has a lone pair of electrons. Ex. NH3

Tetrahedral (SP3): Molecule containing one central atom surrounded by 4 atoms; no lone pairs of electrons on central atom. Ex. CH4

Sub-Atomic Particles

• Electrons (e-)

o 1- charge

o No mass – not part of the atomic mass

o Found around the nucleus in areas of high probability.

• Protons (p+)

o 1+ charge

o 1 amu -- Contributes to the atomic mass

o Found in the nucleus

• Neutrons (n0)

o 0 (ZERO) charge

o ~1 amu – contributes to the atomic mass

o Found in the nucleus

o Made of a proton and an electron (β radiation is the release of the e-)

Unit conversions

(G)iga (M)ega (K)ilo (H)ecta (D)eca unit (d)eci (c)enti (m)illi (μ)icro (n)ano

God! my king Henry died…drinking chocolate milk Monday night

Lab safety

• Review how to read MSDS sheets.

• Report all spills.

• Rinse acid burns with water for 15mins.

• Use gloves, goggles and aprons when working with hazardous materials.

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