Chemistry

Key Terms

Chemistry

The study of matter and the changes it undergoes

Matter

Subatomic Particles ( electrons, neutrons, protons) are the most fundamental building blocks of ____.

Elemental Substance

different substances can be made of only one element

Allotropes

different forms of the same element

Compound

combination of different atoms (elements). Hence, can be broken/decomposed into two or more elements

Pure Substances

Made of the same molecules

Mixture

made of different molecules

Homogenous Mixture

uniform throughout with molecules mixed thoroughly (ex: air or solutions)

Heterogenous Mixture

distinct clumps. Sometimes impossible to mix completely (ex: oil & water)

Physical Property of Matter

(reversible) Can be observed without changing a substance into another substance [ex: solubility, mass, volume, density, boiling point]

Chemical Property of Matter

(irreversible) Can only be observed when a substance changes into another substance [ex: corrosiveness, flammability, reactivity with acid]

Intensive Physical Property

independent of the amount of the substance that is present [ex: density, boiling point, hardness, color, temp]

Extensive Physical Property

dependent on the amount of the substance is present [ex: length, mass, volume, energy, etc]

Physical Change of Matter

changes that do not change the composition of a substance [changes of state, temp., volume]

Chemical Change of Matter

changes that result in new substances [combustion, oxidation, decomposition, etc]

Dimensional analysis

versatile mathematical approach that can be applied to computations ranging from simple unit conversions to more complex-multi step calculations involving several different quantities

Unit conversion factor

ratio of equivalent quantities expressed with different units; used to convert from one unit to a different unit

All Non-zero digits are SIGNIFICANT

True

Zeros in the middle of a number are likely any other digit; they are always significant

True

Zeros are the beginning of the number are NOT significant and are placeholders

True

Zeros at the end of a number and after the decimal point are always significant

True

Multiplication and Division Rule

The answer must contain the same number of significant figures as there are in the measurement with the FEWEST significant figures

Addition and Subtraction Rule

When we add or subtract 2 measurements that answer should contain the same number of decimal places as the measurement with fewest decimal places

Special rounding rule

If the digit you remove is a 5 with nothing following then you can round up to the NEAREST EVEN DIGIT (5.65 —> 5.6) (5.35—>5.4)

Exact Numbers

numbers obtained by counting (no uncertainty associated). They are considered to have infinite significant figures. Definitions/conversion factors are also included.

Precision

how closely a measurement matches the same measurement when repeated

Accuracy

how closely a measurement aligns with a correct value

Atomic number

number of protons in the nucleus of an atom

mass number

the total number of protons and neutrons present in an atom

Isotopes

atoms with the same atomic number but different mass number (isotopes have same chemical properties but different physical properties)

Atomic mass

the weighted average of the isotopes masses of all the naturally occurring isotopes of an element

atomic mass = the sum of (isotopic mass * fractional abundance)

Giga (G)

10^9

Mega (M)

10^6

Kilo (K)

10³

Centi ( c)

10^-2

mili (m)

10^-3

micro (μ)

10^-6

nano (n)

10^-9

pico (p)

10^-12

1 mole of electron

Avogrado’s number: 6.02×10^(23) e

First model of atom

Democritus

Next model of atom (based on experiments) - Atomic theory

John D. Dalton

used:

Antoine Lavoiser: law of conservation of mass (combustion experiments)

Joseph Prout: law of definite proportions

JJ Thomson

Discovered the electron by studying the cathode rays

• created plum pudding model: electrons dispersed in a positive charge cloud

Robert Millikan

debunked plum pudding model with alpha ray scattering

• discovered atomic structure to be: positive particles (protons) concentrated in the center (NUCLEUS)

• electrons revolve around the nucleus (the electrostatic force held atoms together)

James Chadwick

discovered the neutron particle

Photoelectric effect

the emission of electrons from a metal when exposed under electromagnetic radiation

De Broglie

Dual nature of matter (can behave as particles and waves)

• microscopic objects (electrons/protons): have dual nature

• macroscopic objects (ball/car): have no observable wavelength (the greater tha mass, the lower the wavelength), so behave only as particle

λ = h / p

Heisenberg Uncertainly principle

it is impossibel to know accurately and simultaneously both the position and the momentum (velocity) of a moving particle

Δ x Δ p ≥ ℏ / 4pi

Principle quantum number (n)

The n can be any positive integer starting from 1 (n=1,2,3)

describes the SIZE AND ENERGY of the orbital

as the value of n increases, the size & energy of the orbital increases

the number of allowed orbitals with a given n value is n²

all the orbitals with the same n value are said to be in the same SHELL

Angular momentum quantum number (l)

For a given value of n, the l can have values from 0 to n-1

the orbitals with the same l value are said to be in the same SUBSHELL

the angular momentum quantum number defined the 3D shape of the orbital

l=0 (s)

l=1 (p)

l=2 (d)

l=3 (f)

Magnetic quantum number (ml)

described the spatial orientation of the orbital

for a given subshell(l), ml can have values from -l to +l including 0

for a particular subshell with a defined l value, there are 2l+1 possible values of ml

Spin quantum number (ms)

an electron has an intrinsic spin associated with it

2 possible values: +1/2 and -1/2

Pauli exclusion principle

In a given atom, no two electrons can have the same set of the four quantum numbers (n, l, ml, ms).

• as a result, electrons in the same orbital must have the same n, l, ml, and the ms must be different. As a result, there is a maximum of 2 electrons in the orbital (opposite spins)

Aufbau principle

In the ground state of an atom, electrons are filled into the orbitals in the order of their increasing energies (fills ground state followed by higher energy orbitals)

Hund’s rule

when filling electrons into orbitals of equal energy, fill each orbital with a single electron, maintaining parallel spins before doubling up electrons in that orbital set

radial node

a spherical surface where the probability of finding an electron is 0

n-1-l

angular node

a planar surface where the probability of finding an electron is 0

Anomalous electron configuration

occurs because atoms seeks lowest energy state. Having half-filled or completely filled subshells provides extra stability due to symmetry

In group 6B (half-filled): Cr & Mo

In group 11 (1B) completely filled: Cu & Ag

Pattern when removing electrons

np, ns, (n-1)d

Atomic Radius Trend

Generally DECREASE across the period

Generally INCREASES down a group

Isoelectronic series

a series of atoms/ions that have the same number of electrons, so same shielding. Therefore the Zactual (the number of protons) will determine the radius.

Ionization energy

the energy required to remove an electron from a gaseous atom/ion

IE INCREASES across a perios

IE decrease down a group

EXCEPTIONS:

• IE DECREASES from 2A to 3A

• IE DECREASES from 5A to 6A

Electron Affinity

the energy change that occurs when an electron is added to a gaseous atom

Large negatives values—> more likely to gain electron

Large positive value —> unlikely to gain an electron

EA become more negative ACROSS a period

• exceptions: group 2, 5, 8

EA become less negative (more positive) DOWN a group

Lattice Energy

the energy requires to separate one mole of a solid ionic compound into its gaseous ions

the energy released upon forming the crystal from gaseous ions

• size: smaller ions attract more STRONGLY and release more energy compared to larger ions

• charge: Ions wither greater charges attract each other more strongly and release more energy compared to ions with smaller energy

charges have a greater effect on lattice energy

Hydroxide

OH⁻

Hydrogen Sulfate (Bisulfate)

HSO₄^–

Phosphate

PO₄³⁻

Hydrogen phosphate

[HPO₄]^2-

Dihydrogen phosphate

[H₂PO₄]⁻

Hypochlorite

ClO-

Chlorite

ClO₂ ⁻

Chlorate

ClO₃ ⁻

Perchlorate

ClO₄ ⁻

Peroxide

O₂ ⁻²

Acetate

CH₃ COO⁻²

Carbonate

CO⁻²₃

Hydrogen carbonate (bicarbonate)

HCO⁻₃

Permanganate

MnO⁻₄

Ammonium

NH⁺₄

Cyanide

CN^-

Nitrite

NO⁻₂

Nitrate

NO⁻₃

Sulfite

SO⁻²₃

Sulfate

SO⁻²₄

Chromate

CrO⁻²₄

Dichromate

Cr₂O⁻²₇

Electron Pairs

#bonding pairs+ #nonbonding pairs

AX(2)

#bonding pairs: 2

#nonbonding pairs: 0

Electron arrangement: Linear

Molecular shape (bond angle): Linear (180 degrees)

ex: BeCl(2), CO(2), HCN

AX(3)

#bonding pairs: 3

#nonbonding pairs: 0

Electron arrangement: Trigonal Planar

Molecular shape (bond angle): Trigonal Planar (120 degrees)

Ex: BF(3), SO(3), NO(3)-

AX(2)E

#bonding pairs: 2

#nonbonding pairs: 1

Electron arrangement: Trigonal Planar

Molecular shape (bond angle): Bent or “V” shape

Ex: SO(2)

AX(4)

#bonding pairs: 4

#nonbonding pairs: 0

Electron arrangement: Tetrahedral

Molecular shape (bond angle): Tetrahedral (109.5 degrees)

Ex:CH(4), SO(4)2-, ClO4(2-)

AX(3)E

#bonding pairs: 3

#nonbonding pairs: 1

Electron arrangement: Tetrahedral

Molecular shape (bond angle): Trigonal pyramidal (<109.5)

Ex: NH(3)

AX(2)E(2)

#bonding pairs: 2

#nonbonding pairs: 2

Electron arrangement: Tetrahedral

Molecular shape (bond angle): Bent or “V” shaped (104 or <109.5)

Ex: H(2)O,

AX(5)

#bonding pairs: 5

#nonbonding pairs: 0

Electron arrangement: Trigonal bipyramidal

Molecular shape (bond angle): Trigonal bipyramidal

(120 btwn two equatorial positions and 90 degrees btwn axial and equatorial positions)

Ex: PCl(5), SOCl(4), AsF(5)

AX(4)E

#bonding pairs: 4

#nonbonding pairs: 1

Electron arrangement: Trigonal bipyramidal

Molecular shape (bond angle):Seesaw

Ex: SF(4), IF(4+), XeO(2)F(2)

AX(3)E(2)

#bonding pairs: 3

#nonbonding pairs: 2

Electron arrangement: Trigonal bipyramidal

Molecular shape (bond angle): T-shape

Ex: ClF(3), BrF(3)

AX(2)E(3)

#bonding pairs: 2

#nonbonding pairs: 3

Electron arrangement: Trigonal bipyramidal

Molecular shape (bond angle):Linear

AX(6)

#bonding pairs: 6

#nonbonding pairs: 0

Electron arrangement: Octahedral

Molecular shape (bond angle): Octahedral (90 degrees)

Ex: SF(6)

AX(5)E

#bonding pairs: 5

#nonbonding pairs: 1

Electron arrangement: Octahedral

Molecular shape (bond angle): Square Pyramidal

Ex: BrF(5), XeOF(4)

AX(4)E(2)

#bonding pairs: 4

#nonbonding pairs: 2

Electron arrangement: Octahedral

Molecular shape (bond angle): Square planar

Ex: XeF(4), ICl(4)-