basic chemistry review

lecture 0

element

a substance that cannot be broken down into other substances

what do the properties of an element depend on?

the structure of its atoms

compound

a substance consisting of two or more elements

how do the characteristics of a compound relate the the characteristics of its elements?

a compound has characteristics different from those of its elements

what are the four elements most abundantly found in the human body (by percentage of body mass)?

oxygen, carbon, hydrogen, and nitrogen

atom

the smallest unit of matter that retains the properties of an element

what subatomic particles are an atom made up of?

• electrons

• protons

• neutrons

where is most of the mass of an atom located?

in the nucleus, consisting of protons and neutrons

where are the electrons located in an atom?

in a cloud-like orbital around the nucleus

atomic number

number of protons of an atom

atomic mass

number of protons + number of neutrons of an atom

isotopes

two atoms of an element that differ in number of neutrons

stable isotope

nucleus does not tend to lose subatomic particles

radioactive isotope

nucleus decays spontaneously, giving off particles and energy

what happens when radioactive decay leads to a change in number of protons?

the atom is transformed into an atom of a different element

valence electrons

electrons in the outermost orbitals of the atom

ion

an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive or negative charge

chemical bond

a form of attraction between atoms that holds them together

what are the five types of chemical bonds?

• covalent bond

• ionic bond

• hydrogen bond

• van der waals interactions

• hydrophobic interactions

what are the strongest types of chemical bonds?

covalent and ionic bonds

covalent bond

the sharing of a pair of valence electrons by two atoms, where the shared electrons count as a part of each atom’s valence shell

what is the strength of a covalent bond dependent on?

the number of shared electrons (more shared electrons = stronger bond)

molecule

two or more atoms held together by covalent bonds

single covalent bond (single bond)

sharing one pair of valence electrons

double covalent bond (double bond)

sharing two pairs of valence electrons

triple covalent bond (triple bond)

sharing three pairs of valence electrons

electronegativity

an atom’s attraction for the electrons in a covalent bond

nonpolar covalent bonds

atoms share electrons equally

polar covalent bonds

one atom is more electronegative and the atoms do not share electrons equally

ionic bond

difference in electronegativity is so great that the electronegative atom steals the electron from its less electronegative partner

ion

charged atom or molecule

cation

ion with a positive charge

anion

ion with a negative charge

what are the roles and benefits of weak chemical bonds?

• reinforce shapes of large molecules

• help molecules adhere to each other

• reversibility

hydrogen bond

when a hydrogen atom covalently bound to an electronegative atom interacts with an electronegative atom of another molecule

van der waals interactions

attractions between molecules that are close together as a result of asymmetrically distributed electrons in molecules or atoms

hydrophilic

substance with an affinity for water

hydrophobic

substance that does not have an affinity for water

hydrophobic interactions

hydrophobic molecules tend to clump together when in water in order to minimize contact with water