Chapter 2: Basic Chemistry

matter

anything with mass + occupies space

All matter consists of

92 naturally-occurring elements

elements

cannot be broken down into substances with different properties

CHNOPS

Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur → comprise 95% of organisms' body weight

atom

smallest unit of an element that retains its properties

protons

positively charged particles that define the element

neutrons

neutral particles in an atom whose number can vary

electrons

negatively charged particles in an atom whose number can vary

atomic number

number of protons in an atom

mass number

protons + neutrons

both protons and neutrons =

1AMU

atomic mass

weighted average of all isotopes of an element

isotopes

same element, different number of neutrons

unstable isotopes

undergo radioactive decay (release energy)

# of protons usually

equals the # of electrons

valence shell

outermost electron shell of an atom

Bohr Model

1st shell - 2 electrons; outer shells - 8 electrons

octet rule

atoms are most stable when valence shell is full (2 or 8 electrons)

≤ 3 electrons

≥ 5 electrons

→ atoms tend to donate

→ atoms tend to receive

molecule

2+ atoms bonded together

compound

2+ different elements bonded together (ex: CO₂, H₂O, C₆H₁₂O₆)

chemical bonds

caused by interactions between valence electrons

ionic bond

transfer of electrons between donor and acceptor; opposites attract

covalent bond

sharing of electrons between atoms (single, double, or triple bond)

nonpolar covalent bond

equal sharing of electrons (H-H, O-O)

polar covalent bond

unequal sharing of electrons, depends on electronegativity

Electronegativity

ability of an atom to attract electrons

water

polar molecule (not symmetrical)

hydrogen bonds

weak bonds between molecules due to attraction between slightly positive and slightly negative atoms

solvent

most abundant component in a solution

solute

dissolved component in a solution

Hydrophilic

Attracted to water

Hydrophobic

water hating

pure water

neutral

Acid

adds H⁺ ions (ex: HCl → H⁺ + Cl⁻)

Base

adds OH⁻ ions (ex: NaOH → Na⁺ + OH⁻)

pH scale

measure of H⁺ concentration; <7 = acidic, 7 = neutral, >7 = basic

buffers

substances that resist pH changes, maintaining homeostasis in biological systems.

pH < 7.0

pH > 7.8

acidosis

alkalosis

Period

a horizontal row of elements in the periodic table

Group

Vertical column of elements in the periodic table, Contains elements with similar properties because of their simlar electron configurations.

Eletronegativity

the tendency of an atom to attract electrons (or electron density) towards itself

Atom

The most basic unit of matter; the smallest particle of an element

Structure of an Atom

Consists of mostly empty space; Protons (+) and neutrons (0) make up the tiny, dense nucleus. Electrons (-) exist in orbitals at various energy levels surrounding the nucleus. The electrons involved in forming chemical bonds occupy the outermost energy level (AKA the valence shell)

Ion

An atom with a positive or negative electric charge