Chapter 2 Study Guide
Vocabulary:
Word Roots:
an- = not
co- = together
electro- = electricity
iso- - equal
neutr- = neither
pro- = before
Key Terms:
anion: A negatively charged ion
atom: The smallest unit of matter that retains the properties of an element.
atomic mass: The total mass of an atom, which is the mass in grams of one mole of
the atom.
atomic nucleus: An atom’s central core, containing protons and neutrons.
atomic number: The number of protons in the nucleus of an atom, unique for each
element and designated by a subscript to the left of the elemental symbol.
cation: An ion with a positive charge, produced by the loss of one or more electrons.
chemical bond: An attraction between two atoms, resulting from a sharing of outershell electrons or the presence of opposite charges on the atoms. The bonded atoms
gain complete outer electron shells.
compound: A substance consisting of two or more elements in a fixed ratio.
covalent bond: A type of strong chemical bond in which two atoms share one or
more pairs of valence electrons.
electron: A subatomic particle with a single negative charge. One or more electrons
move around the nucleus of an atom.
electron shell: An energy level represented as the distance of an electron from the
nucleus of an atom.
electronegativity: The attraction of an atom for the electrons of a covalent bond.
element: Any substance that cannot be broken down to any other substance.
energy: The capacity to do work (to move matter against an opposing force).
hydrogen bond: A type of weak chemical bond formed when the slightly positive
hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly
negative atom of a polar covalent bond in another molecule.
ion: An atom that has gained or lost electrons, thus acquiring a charge.
ionic bond: A chemical bond resulting from the attraction between oppositely
charged ions.
ionic compound: A compound resulting from the formation of an ionic bond; also
called a salt.
isotope: One of several atomic forms of an element, each containing a different
number of neutrons and thus differing in atomic mass.
mass number: The sum of the number of protons and neutrons in an atom’s
nucleus.
matter : Anything that takes up space and has mass.
molecular formula: A type of molecular notation indicating only the quantity of the
constituent atoms
molecule: Two or more atoms held together by chemical bonds
neutron: An electrically neutral article (having no electrical charge), found in the
nucleus of an atom.
non-polar covalent bond: A type of covalent bond in which electrons are shared
equally between two atoms of similar electronegativity
orbital: The three-dimensional space where an electron is found 90% of the time.
polar covalent bond: A covalent bond between atoms that differ in
electronegativity. The shared electrons are pulled closer to the more
electronegative atoms, making it slightly negative and the other atom slightly
positive
potential energy: The energy stored by matter as a result of its location or spatial
arrangement.
proton: A subatomic particle with a single positive electrical charge found in the
nucleus of an atom.
radioactive isotope: An isotope that is unstable; the nucleus decays spontaneously,
giving off detectable particles and energy
salt: A compound resulting from the formation of an ionic bond; also called an ionic
compound
structural formula: A type of molecular notation in which the constituent atoms are
joined by lines representing covalent bonds
trace elements: An element indispensable for life but required in extremely minute
amounts.
valence: The bonding capacity of an atom, generally equal to the number of
unpaired electrons in the atom’s outermost shell.
valence electron: An electron in the outermost electron shell.
valence shell: The outermost energy shell of an atom, containing the valence
electrons involved in chemical reactions of that atom.
Chapter 2 Important Points:
Matter is anything that takes up space and has mass.
 It is comprised of elements which may be individual or combined in various
ratios to form compounds or molecules.
 An element is something that can not be further broken down by just typical
chemical reactions so once you go below the level of matter, you are dealing
with subatomic particles
There are 92 naturally occurring elements. Most living organisms are made of just
four: carbon, hydrogen, oxygen and nitrogen
The atom can be broken into 3 main parts:
 Protons, found in atomic nucleus, positively charged
 Neutrons, found in atomic nucleus, electrically neutral
 Electron, found surrounding atomic nucleus in series of electron shells,
negatively charged
Atomic number = number of protons in an atom
 Also number of electrons in neutral atom
 Each element has a unique atomic number
Mass number = number of protons + number of neutrons
Isotopes are varieties of the same element which have the same atomic number
(thus same proton number) but different mass numbers (thus different number of
neutrons)
Valence electrons are those in the outermost electron shell of an atom.
 They are the only electrons involved in bonds with other atoms
 Valence number is the number of unpaired valence electrons and determines
how many bonds an atom can form with other atoms
Electrons are found in certain areas called orbitals 90% of the time
 1st electron shell has one s (1s) orbital
 2nd electron shell has one s (2s) orbital and three p (2p) orbital
 Each orbital can hold maximally 2 electrons so 1st shell can potentially hold
total of 2 electrons; 2nd shell can potentially hold a total of 8 electrons
 Inert elements have complete valence shells and don’t interact with other
atoms
Atoms can complete their valence shells by sharing electrons with other atoms
(covalent bonds) or by losing or gaining electrons (forming ions or charged atoms)
Polar covalent bonds occur between atoms that have different electronegativity
values (electronegativity is the measure of how strong an atom attracts shared
electrons)
Non-polar covalent bonds occur between atoms that have equal electronegativity
values
A single covalent bond is one pair of electrons shared between atoms
A double covalent bond shares 2 pairs of electrons.
Molecular formulas show which elements and how many are found in a molecule.
Structural formulas show additionally the physical arrangement of atoms in a
molecule.
Ions forms when electrons are transferred between atoms.
 Atoms that gain electrons and become negatively charged are called anions.
 Atoms that lose electrons and become positively charged are called cations.
 Anions and cations attract each other, forming ionic bonds
 Ionic compounds or salts are formed between ions.
Hydrogen bonds are weak, transient bonds formed between polar molecules due to
slight positive and negative charges caused by polar covalent bonds within the
molecules.