anion
An ion with a net negative charge
Anions have gained electrons. With more electrons than protons, these ions have an overall negative charge.
atomic number
The number of protons in each atom of an element
Each element has a unique atomic number. In neutral atoms, this is also the number of electrons.
cation
An ion with a net positive charge
Cations have donated electrons. With more protons than electrons, these ions have an overall positive charge.
chemical bond
An attractive force that holds two atoms together
Chemical bonds are broken or formed during chemical reactions.
compound
A substance made up of two or more types of atom bonded together
Water is a compound with molecules made of one oxygen atom bonded to two hydrogen atoms.
covalent bond
An attraction between atoms that share electrons
Covalent bonds form when two non-metal atoms share valence electrons.
electron configuration
The arrangement of electrons in shells around an atom’s nucleus
Nitrogen has the configuration 2.5 while magnesium has the configuration 2.8.2.
electron shell
A grouping of electrons around the nucleus of an atom
Electron shells increase in energy level with distance from the nucleus.
group
A column in the periodic table
Elements in the same group have the same number of valence electrons and tend to have similar properties.
ion
An atom or molecule with a net charge
A neutral atom that gains an electron becomes a negative ion with a charge of –1.
ionic bond
An electrostatic attraction between ions with opposite charges
Ionic bonds form when metal atoms transfer electrons to non-metal atoms, forming cations and anions.
lattice
A repeating arrangement of atoms in a solid
Lattices are highly ordered structures held together by bonds between atoms.
metal
A shiny, malleable element that conducts heat and electricity
Metals include magnesium and calcium. They tend to form cations by losing valence electrons.
molecule
A group of atoms bonded together
An oxygen gas molecule is made up of two oxygen atoms bonded together.
neutral atom
An atom with no net charge
An atom is neutral when it has an equal number of protons and electrons.
noble gas
An element that is non-reactive due to its full valence shell
The noble gases have full valence shells so they don’t tend to form chemical bonds with other atoms.
non metal
A dull, brittle element that does not conduct heat or electricity
Non-metals include sulfur and oxygen. They tend to form anions by gaining valence electrons.
period
A row in the periodic table
Elements in the same period have the same number of electron shells.
periodic table
A grid arrangement of all known elements in order of atomic number
The modern periodic table was developed by Dmitri Mendeleev in the 1860s.
reactivity
A substance’s tendency to chemically interact with other substances
Reactivity trends in the periodic table are explained by atomic radius and attractive forces on valence electrons.
valence electron
An electron in the outermost occupied shell of an atom
Valence electrons can be transferred or shared with other atoms to form chemical bonds.
valence shell
The outermost occupied shell of an atom
Atoms form bonds to obtain full valence shells. They can do this by transferring or sharing electrons.
