CH.5 - Chemistry Key Concept

The Law of Constant Composition

Elements combine in fixed proportions to form compounds.

—> The ratio determines what kind of compound the substance is.

Chemical Formulas

An expression of the number of and types of atoms in a molecule

Molecule

A particle composed of 2 or more nonmetal atoms

• EX: H2SO4 ←- Nonmetals

Ionic Compound

A particle composed of a metal and nonmetal atom

Format of a Chemical Formula

1. Chemical formulas list the most metallic elements first

2. In compounds, the most metal-like (LEFT) element is listed first

3. If an element is in parentheses, then that is intended to clarify atomic composition

Molecular Chemical Formula

To use chemical symbols to indicate the types of atoms followed by subscripts to show the number of atoms of each type in the molecule

Empirical

Types of atoms present and the simplest whole-number ratio of the number of atoms/ions in the compound

Structural Chemical Formula

Same as the molecular formula, but focuses on how the atoms are connected in the molecule

Isomers

Compounds with the same chemical formula, but different molecular structures

• Elements bond differently —> may look the same but are not the same when mirrored.

Structural Isomers

Compounds in which the molecules differ in how the atoms re connected to each other

Spatial Molecule

The relative orientations of the atoms in space are different

• Some formula and connection, just different spatial orientations

• —> Mirror images result in different interactions, which leads to a different orientation

Elements and Compounds: Atomic

One type of element

• Retains all of the element's unique chemical properties (e.g. atomic number)

Elements and Compounds: Molecular

Any group of two or more atoms bonded together

• Two nonmetals

Elements and Compounds: Ionic

A charged particle that occurs after an atom gains or loses its electrons

• Nonmetal + Metal

Elements and Compounds: Diatomic Molecules/Diatomics

The co-existence of elements as 2 atom molecules

• One cannot exist without the other!

• EX: Hydrogen, Nitrogen, Oxygen, Florine, Cl, Br, I…

Elements and Compounds: Ionic Compounds

To contain one or more cations paired with one or more anions

• Often involve a metal + nonmetal

• EX: NaCl, AlBr3, K2SO4

Elements and Compounds: Covalent (Molecular) Compounds

Form when nonmetallic elements share valence electrons to achieve stable octet.

• Formed from two or more nonmetals

• EX: H2O, CO2, CH4

Formula for Mass

Average mass of the molecules that compose a compound

• Formula Mass = (amount of atoms of 1st element x atomic mass of 1st element) + (amount of 2nd element x Atomic mass of 2nd element)

Octet Rule

The tendency for atoms to give or transfer electrons to obtain a stable configuration of eight (8) valance electrons.

• Associated with the stability of NOBLE GASES

• By forming an octet, atoms become more stable

• Helium is the exception :3

Ionic Compounds

Formed when metal atoms transfer electrons to nonmetal atoms

• Results in the formation of an IONOIC BOND

• One atom gives or takes an electron. (exchange)

Molecular/Covalent Compounds

Formed when nonmetals share valance electrons

• Atoms share rather than give/take electrons

Metals and Ionic Bonding

Metals LOSE ELECTRONS and becomes CATIONS

• Give up an electron to have a more positively charged subatomic structures (protons)

• Goal is to get rid of electrons

Nonmetals and Ionic Bonding

Nonmetals GAIN ELECTRONS and becomes ANIONS

• Goal is to gain electron