Chemistry Regents Comprehensive Review revised 2026

Protons

Positive charge particle; 1 amu; located in the nucleus

Neutron

neutral; 1 amu; located in the nucleus

electron

negative charge; tiny mass; located in orbitals outside the nucleus

Mass number

Protons and neutrons added together

Atomic number

number of protons

How is the periodic table arranged?

Its arranged in order of increasing atomic number

How do you determine the number of neutrons?

Subtract the mass number from the atomic number

Dalton's atomic model

One of the initial atomic models, atoms were solid spheres

Element

Pure substance, made of one type of atom

Compound

Pure substance; made of two or more different elements in a fixed proportion

Diatomic element

HONClBrIF; still a pure element, two of the SAME element chemically bonded

JJ Thompson

discovered the electron, plum pudding model

Rutherford's gold foil experiment lead to the discovery that atoms

were mostly empty space with a small dense positively charged nucleus

Bohr's model showed that

the nucleus was small, dense, positive, with electrons that moved in circular orbits around the nucleus

Wave mechanical model says that

electrons move in an electron probability cloud around the nucleus

Wave mechanical model says that orbitals

are areas where an electron is MOST LIKELY to be found.

Each atoms is made of a....

positively charged nucleus with orbiting negatively charged electrons on the OUTSIDE

Protons and neutrons are located

IN THE NUCLEUS

In an ATOM the number of protons equals the number of

electrons; the positive charges are cancelled by the negative charges to make a NEUTRAL charge

Average atomic mass is calculated using

natural abundances of isotopes and relative masses of the isotopes

Isotope

same number of protons DIFFERENT number of neutrons

Where do I find polyatomic ions on the reference table?

ions that have more than one atom; now found on page 3, "Selected Ions Forming Aqueous Solutions"

Ground state

when all electrons are in their lowest possible energy level, with the first orbital having the least amount of energy

Excited state

When an electron gains energy it moves up to a higher energy level

Electrons that move from the ground state to the excited state

electrons must absorb energy to move from a lower energy level to a higher energy level

In terms of electrons, how could an atom emit colored light?

When excited electrons fall to a lower energy level, they can release energy in the form of light called Spectra

Bright line spectrums can be used to identify elements because

bright line spectra are UNIQUE to every element, this only depends on the element, not amount!

Valence electrons

are the outermost electrons; they determine the chemical properties of an atom and how it will form bonds with other elements

Elements in the same group have similar chemical properties because

elements in the same group have the same number of valence electrons and form bonds the same

Atoms with a filled valence shell

are stable; they will not react with other elements

Noble gases do not react because

they have full valence shells and stable electron configurations

Noble gases are located in

group 18! Helium, neon....

STP

Standard temperature and pressure, first page of your reference table

Atoms of the same element all have the

same number of protons in their nucleus

Nuclear charge is determined by

the number of protons in the nucleus of an atom, you can look at the atomic number on the periodic table; p+ + n0 = nuclear charge (+)

Changing the number of protons in a nucleus...

changing the number of protons in an element will change the identity of the element

Transmutation

changing the protons in the nucleus changes the atom to a NEW type or DIFFERENT type of elements when a particle is emitted

Stability of an isotope depends on

the ratio of protons to neutrons

Most radioactive elements have an atom number of

83 or above!

Symbols Used in Nuclear Chemistry

types of particles, mostly in decay, as well as their masses and charges; page 3 of the 2025 NYSCRT

Fission reactions

Split a heavy nuclei into smaller ones

Fusion reactions

occur when light nuclei combine into heavier nuclei; produces the most energy but difficult to replicate

In nuclear reactions, mass is converted into

large amounts of energy! Think of nuclear bombs (fission) or the sun (fusion)

Artificial transmutation

requires the bombardment of a nucleus by high energy molecules

Risks with radioactive or nuclear reactions can be

biological exposure (cancer poisoning), long term storage, disposal and nuclear accidents

C - 14 isotope is used for

carbon dating of once living organisms

U - 238

geological dating of planets and rocks

I -131

treatment of thyroid disorders

Co - 60

cancer treatments and kill tumors

Atomic radii

distance from the nucleus to the outermost electron aka how big an atom is, increase as you go down a group because electrons shells are being added

Ionization energy

amount of energy required to completely REMOVE an electron

Electronegativity

attraction to an electron

Lewis dot diagram

draw valence electrons around an element symbol (no more than 2 per side for a total of 8)

Metallic properties

malleable, lusterous, conduct electricity as a solid

Nonmetal properties

dull, brittle, do not conduct electricity

Allotropes of carbon (Like diamond and graphite)

have different structures and different properties (Carbon)

O2 (oxygen) and O3 (ozone) have.....

different structures and different properties (Oxygen)

Breaking a bond is an....

ENDOTHERMIC PROCESS, you must gain energy (bonding)

Forming a chemical bond is an..

EXOTHERMIC PROCESS, you go to a more stable state (bonding)

Ionic bonding

between a METAL and NONMETAL, electrons are transferred here

Atom gains an electron....

it becomes a negative ion with a larger radius ex) F + e- --> F-

Atom loses an electron

it becomes a positive ion with a smaller radius (usually due a loss in a shell) Ex) Na --> Na+ + e-

(molecular) Covalent bonding

between two nonmetals; electrons are shared

Ionic substance properties

high MP and BP; form crystals, dissolve in water (Table F) and conduct electricity in solution and as a liquid

Ionic substances conduct electricity when dissolved or melted because

ionic substance dissolve into MOBILE FREE MOVING ions. These ions can move freely

Covalent substance properties

never conduct electricity, tend to be soft, low MP and low BO

Metallic bonding

is described as a sea of free moving electrons, resulting in metals being malleable, conductive

How do you determine if an ionic compound is soluble or insoluble?

Selected Ions Forming Aqueous Solutions on page 3 of your NYS Chemistry Reference Table (NYSCRT)

Polar substances dissolve

only in other polar substances (like dissolves like)

Nonpolar substances dissolve

only in nonpolar substances (like dissolves like)

Single covalent bond has...

1 pair of shared electrons, or 2 electrons being shared

Double covalent bond

2 pair of shared electrons; 4 electrons are being shared total

Triple covalent bond

3 pairs of shared electrons, 6 electrons are being shared in total

HONC

H-1; O-2; N-3; C- 4

Polarity of a bond is determined by

subtracting two electronegativities values, a high difference (o.5 - 1.9999) is POLAR; (0.4 and below) is NONPOLAR

Polar bond forms if

the difference in EN is higher than 0.4

Nonpolar bonds form if

the same element is bonded or if the EN difference is lower than 0.4

Polarity if a molecule is determined by

determining symmetry of the entire molecule

A nonpolar molecule has a

symmetrical shape and has a symmetrical or even distribution of charge

A nonpolar molecule with polar bonds can occur

if the charge is distributed symmetrically, like CH4 or CO2

A polar molecule has an

asymmetrical shape and has an asymmetrical or UNEVEN distribution of charge

Ionic compounds with polyatomic ions have both....

IONIC and COVALENT bonding, use table E to check this bonding

Intermolecular forces

Force of attraction between individual molecules

A higher boiling point, high melting point, all result from

strong intermolecular forces, the stronger the IMF the higher the BP

Hydrogen bonds

are intermolecular forces NOT BONDS; the occur when hydrogen bonds with N...O...F

hydrogen bond result in

the high boiling point of water, these are strong IMFs between water

Iodine is a solid at STP while Neon is a gas at STP because

Iodine has stronger intermolecular forces, resulting in a higher melting and boiling point.

Mixtures...

are made from two or more different substances in a random/varied proportion

homogenous mixture

even or uniform distribution of particles, evenly mixed you usually cant see the difference in particles

Heterogenous mixture

uneven or nonuniform distribution of particles, you can see differences here

Because parts of the mixture maintain their physical properties

You can use differences in particle size, polarity, density, MP, BP and solubility to separate mixture

Distillation

separation of a mixture by boiling point (mixture of oils, alcohols and water)

Filtration

separation of a mixture by particle size and solubility (salt water and sand)

Chromatography

Separation of mixture by polarity and size

evaporation

separation of mixture by solubility

Elements with the same atomic number cannot be.....

cannot be broken down by chemical changes, only nuclear

Compounds can be

can be broken down and separated by chemical changes; different properties from elements that it is composed of

Mixtures can be

can be separated by physical means and maintain their properties

Chemical change results in

a rearrangement of atoms forming or breaking bonds; you will see a difference in the bonding and position of these particles

Physical changes result in

atoms are moved around, no bonds are broken or made, usually shown with a phase change like melting... boiling