Lecture 7: Electron Affinity, Ions , and Compounds & Molecules

electron affinity

the negative energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion, how likely an atom is to except an electron; atoms with low _____ tend to be cations; atoms with high _____ tend to be anions

exothermic

process that releases heat, causing the temperature of the immediate surroundings to rise; a negative value of [delta]H is _____ [ex. F(g) + e- ---> F-(g)]

endothermic

process that absorbs heat and cools the surroundings, happens only in concert with one or more exothermic processes such as forming an ionic compound (since that process requires energy)

metals

elements whose atoms tend to lose electrons during a chemical change

noble gases

group on the periodic table with full ns and np subshells, making them very stable and tend not to accept/give up electrons

isoelectric

when two ions share the same electron configuration, but different nuclear charges

ionic radius

the radius of a cation or anion; cations are always smaller than their atoms and anions are always bigger than their atoms (the radius increases due to electron-electron repulsions)

compound

substance composed of two or more elements combined in a specific ratio and held together by chemical bonds

molecule

bonded by the sharing of electrons --> covalent bonds; the simplest structural unit of an element or compound

ionic compound

a pure substance formed between a metal and a nonmetal that has an overall neutral charge --> NO molecules in a(n) _____

diatomic molecules

molecules that contain 2 or more atoms; are either heteronuclear (two different elements) or homonuclear (two of the same elements)

polyatomic molecules

contain two or more atoms

chemical formula

formula that denotes the composition of a substance; i.e. H2O

molecular formula

formula that shows the exact number of atoms of each element in a molecule; i.e. H:O:H or H-O-H

structural formula

formula that shows the element composition and the general arrangements

law of conservation of mass

the law that mass cannot be created or destroyed, mass is constant during ordinary chemical reactions, atoms present at the start of the reaction must be present after reaction

law of definite proportions

the law that a chemical compound has a fixed ratio of component elements

law of multiple proportions

the law that says (in short) that there cannot be a fraction of an atom

molecular weight

sum of atomic masses (in g/mol) in a molecule