Intro Chem I Exam 2

What periodic trend is generally observed for Z_effective?

Left to right: increases

Down a column: decreases

What periodic trend is generally observed for the size of neutral atoms?

Left to right: decreases

Down a column: increases

What periodic trend is generally observed for first ionization energy of an atom?

Left to right: increases

Down a column: decreases

What periodic trend is generally observed for electron affinity?

Left to right: increases

Down a column: decreases

How do you estimate the Z_effective?

Z_effective = Z-S

Z= atomic number

S= number of core electrons

What correctly describes the Z_eff experienced by a 2s and 2p electron of boron?

The 2s electron has a greater Z_eff than a 2p electron because it is closer to the nucleus and experiences less shielding from core electrons.

How do you write electron configurations for ions?

Add or subtract electrons from the highest n quantum level and then the highest l quantum level.

How do you determine the size of ions and rank them from smallest to largest?

Step 1:

Write out electron configurations; more energy levels mean it is larger

Step 2:

If they are isoelectronic, then more protons mean it is smaller

When are there large jumps in ionization energies?

When an electron is removed from one of the core electrons

What does a positive electron affinity mean?

Adding an electron is unfavorable and requires energy

What does a negative electron affinity mean?

Adding an electron is favorable and releases energy.

What does 0 electron affinity mean?

Adding an electron is neither favorable nor unfavorable, resulting in no energy change.

Ionization Energy (I)

minimum energy required to remove an electron from an atom

Ionization Energy Trend

I₁<I₂<I₃<I₄…

Reactants

The starting substances in a chemical reaction

Products

The substances formed as a result of a chemical reaction

(g)

indicates that a substance is in the gaseous state.

(s)

indicates that a substance is in the solid state.

(l)

indicates that a substance is in the liquid state.

(aq)

indicates that a substance is in aqueous solution, meaning it is dissolved in water.

You can only change the ________ when balancing equations

coefficient

How to balance a chemical equation

Adjust coefficients on both sides so that the number of atoms for each element is equal.

(Start by adjusting the coefficients for the most complex molecule)

Molar Mass

mass of 1 mole of a substance

Molar mass is equal to…

atomic mass, the units are just different

unit for atomic mass

amu

unit for molar mass

g/mol

1 mol is equal to

Avogadro’s number: 6.022 × 10²³ things (such as atoms, electrons, ions, etc.)

Steps on how to find emprical formulas from analyses

Step 1: Convert mass percentages to grams (100 g)

Step 2: Convert grams to moles by using the molar mass of each element.

Step 3: Divide the moles of each element by the smallest number of moles obtained.

Step 4: If necessary, multiply the resulting ratios by a small whole number to obtain whole-number ratios.

Hydrogen

atomic number: 1

symbol: H

Helium

atomic number: 2

symbol: He

Lithium

atomic number: 3

symbol: Li

Beryllium

atomic number: 4

symbol: Be

Boron

atomic number: 5

symbol: B

Carbon

atomic number: 6

symbol: C

Nitrogen

atomic number: 7

symbol: N

Oxygen

atomic number: 8

symbol: O

Fluorine

atomic number: 9

symbol: F

Neon

atomic number: 10

symbol: Ne

Sodium

atomic number: 11

symbol: Na

Magnesium

atomic number: 12

symbol: Mg

Aluminum

atomic number: 13

symbol: Al

Silicon

atomic number: 14

symbol: Si

Phosphorous

atomic number: 15

symbol: P

Sulfur

atomic number: 16

symbol: S

Chlorine

atomic number: 17

symbol: Cl

Argon

atomic number: 18

symbol: Ar

Potassium

atomic number: 19

symbol: K

Calcium

atomic number: 20

symbol: Ca

NH₄⁺

ammonium

NO₃^-

nitrate

NO₂^-

nitrite

SO₄^2-

sulfate

SO₃^2-

sulfite

ClO₄^-

perchlorate

ClO₃^-

chlorate

ClO₂^-

chlorite

ClO^-

hypochlorite

CO₃^2-

carbonate

PO₄^3-

phosphate

combination reaction

When two or more substances combine to form a single product.

A + B → AB

combustion reaction

When a substance reacts with oxygen to produce energy, resulting in the products carbon dioxide and water.

hydrocarbon + O₂ → CO₂ + H₂O

decomposition reaction

When a single compound breaks down into two or more simpler products.

AB → A + B

single-replacement reaction

When an uncombined element takes the place of another element in a compound.

A + BC → AC + B

How do you find molecular weight?

sum the atomic weights of all atoms in the molecule based on its chemical formula

Given the grams of a compound, how would you find how many molecules are in it?

Step 1: Divide the grams by the molecular weight to find moles

Step 2: Multiply by Avogadro's number.

How to calculate percentage by mass

Divide the mass of the element by the total mass of the compound

Whole-number multiple formula

molecular weight/empirical formula weight

How do you find the molecular formula from the empirical formula?

Step 1: Find the whole-number multiple

Step 2: Multiply the subscripts in the empirical formula by the whole-number multiple

How do you find the grams of something produced when given the mass of a reactant?

Step 1: Convert the reactant’s mass to mols

Step 2: Using the coefficients from the balanced equation, convert from mols of the reactant to mols of the product

Step 3: Convert the product's mols to mass