Chapter 4: Chemical Bonding and Molecular Geometry

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

Lewis Dot Symbols: consists of the element’s symbol plus dots

    -Each dot represents a valence electron

    -When atoms form compounds, it is their valence electrons that interact

   -Maximum stability results when a chemical species is isoelectronic with a noble gas

    -Main group metals: the number of dots is the number of electrons lost

    -Nonmetals: the number of unpaired dots is the number of bonds the atom can form

    -Ions may also be represented by Lewis dot symbols

Isoelectronic: different atoms that possess the same number of electrons, resulting in similar electron configurations and similar chemical properties

    -The elements are trying to gain or lose electrons for a complete octet

LEO: Lose Electrons Oxidation

    -Metals lose electrons and become positive

GER: Gain Electrons Reduce

    -Nonmetals gain electrons and become negative

Ionic bonding refers to the electrostatic attraction that holds oppositely charged ions together in an ionic compound

    -Ionic bonding: transfer or exchange of electrons

A chemical formula or formula of an ionic compound denotes the constituent elements and the ratio in which they combine

Lattice: three-dimensional array of oppositely charged ions

Lattice energy: the amount of energy required to convert a mole of ionic solid to its constituent ions in the gas phase

The formation of ionic bonds releases a large amount of energy

    -The magnitude of lattice energy is a measure of an ionic compound’s stability

    -Lattice energy depends on the magnitudes of the charges and on the distance between them

Force decreases as ions get bigger

A monatomic cation is named by adding the word “ion” to the name of the element

A monatomic anion is named by changing the ending of the element’s name to “-ide” and the word ion

Ionic compounds are electronically neutral

This balance of positive and negative charges is crucial for the stability of the compound.

    -In order for ionic compounds to be electronically neutral, the sum of the charges on the cation and anion in each formula must be zero

Covalent Bonding: compounds formed between elements with similar properties, electrons are shared in order to give each atom a noble gas configuration

    -This approach leads to Lewis’ theory of bonding, which proposes that electrons are arranged in pairs around atoms, helping to predict molecular structure and bonding effects

    -Molecule: is a combination of at least two atoms in a specific arrangement held together by chemical forces (chemical bonds)

    -Law of definite proportions: states that a chemical compound, regardless of its source or how it was prepared, will always contain the same proportion of elements by mass.

    -Law of multiple proportions: two elements can form two or more different compounds

            -This tells us the ratio of masses of one element that combine with a fixed mass of the other element

Diatomic molecules: contain two atoms and may be either heteronuclear or homonuclear

Polyatomic molecules: contain more than two atoms

Chemical formula: denotes the composition of the substance

Molecular formula: shows the exact number of atoms of each element in a molecule

Allotropes: elements have two or more distinct forms

Structural formula: shows elemental composition and general arrangement

Empirical formula: the whole-number ratio of elements → simplest formula

Naming molecular compounds: name the first element, and then name the second element, and change the ending to -ide

        -Greek prefixes used to denote the number of atoms of each element present (1-10)

        - Hydrogen does not usually conform to the systematic naming guidelines

Acid: substance that produces hydrogen ions when dissolved in water

    -Combine the two names and drop the -gen in hydrogen, and drop the -ide in the second element and change it to -ic

Inorganic compounds: generally defined as those without carbon

Organic compounds: contain carbon and hydrogen → sometimes in combination with other atoms

Hydrocarbons: contain only carbon and hydrogen

Simplest hydrocarbons are called alkanes

Many organic compounds contain groups of atoms known as functional groups, which determine a molecule’s reactivity

Ions must combine in a ratio that give a neutral formula overall

Oxoanions: polyatomic anions that contain one or more oxygen atoms and one atom (‘the central atom’) of another element

    -monoprotic: (one ionizable hydrogen)

    -polyprotic (more than one ionizable hydrogen)

Hydrate: a compound that has a specific number of water molecules within its solid structure

Anhydrous: means the compound no longer has water molecules associated with it

IONIC COMPOUNDS DIVIDE THROUGH TO GET SIMPLEST RATIO we do NOT do this for covalent

Molecular mass: mass in amu of an individual molecule

Molecular weight: average molecular mass of a compound calculated from the weighted average of the isotopes of its constituent elements

Formula mass: mass of formula unit sometimes called formula weight (for ionic compounds)

Percent composition by mass: a list of the percent by mass of each element in a compound

Molar mass: the mass in grams of one mole of the substance