Key Terms
Matter
Anything with mass that occupies space. Element: a pure substance that cannot be broken down by ordinary chemical reacti
Atom
Smallest unit of matter that retains an element's chemical properties.
Atomic number
Number of protons. Defines the element.
Isotopes
Same element, different neutron count. Same protons, different mass.
Example
Carbon-12 has 6 protons + 6 neutrons. Carbon-14 has 6 protons + 8 neutrons.
Radioisotopes
Unstable isotopes that emit particles and decay to a more stable form.
Octet rule
Atoms are most stable when the outermost (valence) shell has 8 electrons. The innermost shell is the exception (stable a
Valence shell
The outermost electron shell. Determines how an atom bonds.
Polar covalent bonds
Electrons shared unequally. One atom is more electronegative and pulls electrons closer.
Nonpolar covalent bonds
Electrons shared equally. Same element bonded to itself (O2) or similar electronegativities (C-H in methane).
BOND STRENGTH RANKING (strongest to weakest)
Triple covalent > Double covalent > Single covalent > Ionic > Hydrogen > Van der Waals
Reactants
Starting substances (left side of equation). Products: ending substances (right side).
Law of conservation of matter
Atoms are neither created nor destroyed. Balanced equations have equal atom counts on both sides.
Irreversible reactions
Go in one direction; reactants used up completely. Reversible reactions: can go both directions; reach equilibrium when
Hydrophilic
Water-loving. Polar or charged molecules.