Cram Unit 1: Atomic Structures and Properties

Atom

the smallest unit of matter; they are always neutral p+=e-

Nucleus

protons (+) and neutrons (neutral)

Electrons

Negatively charged; surround the nucleus.

Atomic number

The number of protons

Atomic mass

Protons + neutrons

Isotope

Different forms of atoms for the same element with same number of protons and different number of neutrons.

Mass spectroscopy

• (% of abundance * mass of the isotope) +(% of abundance * mass of the isotope)…= average atomic mass of an element.

Estimating average atomic mass

You can add the numbers on top to find the percentage of abundance by multiplying (70 × 9/9+6+1)+(72 × 96/9+6+1)… OR find the in-between of the largest columns, here it would be 70 and 71. This means the amu should be around 71.

Classifying Matter

What are the pure substances?

They have invariant chemical composition and have distinct properties. elements and compounds

What are the mixtures?

Two or more pure substances that retain their original identities and can be separated by physical means. Homogeneous and heterogeneous

Element

fundamental substances; cannot be separated into simpler substances. (Cu, Zn, Ag or O2, H2, N2, O3)

Compound

two or more elements in fixed proportions and can be separated into simpler substances/elements by chemical means. (CuO, H2O, CH3CH2OH)

Homogeneous

They have a uniform composition and properties throughout (also called a solution) (Saline water)

Heterogeneous

They are not uniform in composition and properties all throughout. (Salad)

How do we separate mixtures that are completely soluble?

Through evaporation or distillation.

Molar mass (g/mol)

mass of any substance for 1 mole (Atomic mass)

Molar mass for a compound

Just add up the sum of the molar masses respective to the ratio.

Avogrado’s Number

6.022 X 10(23)

Mass

Number of moles * Molar mass

Number of particles

Number of moles * Avogrado’s Number

Number of moles

Mass of the sample / Molar mass

Empirical and Molecular Formula

Molecular C6H12O6 (6:12:6) → Empirical CH2O (1:2:1)

How to calculate molecular formula

Empirical formula + molar mass

• Find the molar mass of the empirical formula

• Divide the empirical formula molar mass by the molar mass given

• Multiply the result to each of the atoms in the empirical formula

Atomic structure

• Atom= electrons, protons, and nucleus

• Electrons are in specific shells (energy levels) and subshells (sublevels)

Energy shells

n= 1, n=2, n=3, n=4….

Valence electrons

Reside in the outermost shell

Subshells

s, p, d,f

• Energy increases from s → f

Shell 1

s

Shell 2

s, p

Shell 3

s, p, d

Shell 4

s, p, d, f

s

2 electrons

p

6 electrons

d

10 electrons

f

14 electrons

s

1 orbital

p

3 orbitals

• Hold two electrons each

Electron configuration

Aufbau principle: electrons first occupy those orbitals whose energy is the lowest.

Hund’s Rule

The lowest energy configuration for an atom is the one having the maximum number of unpaired electrons within the same energy sublevel.

Photoelectron spectroscopy

Represents electron distribution and energy

• X-axis: Binding energy (energy necessary to remove an electron)

• To the left → Closer to the nucleus

• To the right → Closer to the valence shell

• Y-axis: # of electrons

Periodic Trends

Atomic radius, ionization energy, electron affinity, electronegativity

Coulomb’s Law

It indicates that forces of attraction depend on the distance and magnitude of the charges.

• Greater distance → Less force

• Greater magnitude → More force

Atomic radius

• As we go down a group, atomic radius increases because there will be more energy levels, maximizing the distance between the nucleus and the valence electrons. Also explained by forces of repulsion as electrons increase, so does the electron shield.

• As we go right a period, the atomic radius decreases because the number of protons also increases, creating greater magnitude, thus creating greater forces of attraction.

Ionic radius

• If they lose electrons, they become smaller.

• If they gain electrons, they become larger.

First ionization energy

The amount of energy required to remove an electron.

Ionization energy trend

• As electrons are closer to the nucleus, energy increases because of the high nuclear charge.

• As electrons are farther away from the nucleus, energy decreases because of the weaker nuclear charge.

It is likely that ionization energy will be lower if the subshell is not…

fully-filled.

Electron affinity

The energy change that occurs when an atom gains an electron.

Electronegativity

The ability of an atom to attract electrons.

• Increases from left to right because effective nuclear charge increases

• Decreases down a group because there are more shells, creating less attractions between the nucleus and electrons.