Chapter 2- Atoms, Elements, and Compounds

Atom

smallest unit of matter that retains the properties of a chemical element.

Element

smallest part of a substance that can exist on its own.

Compound

When two or more chemical elements chemically bond together.

Mixture

Contains more than one substance (elements or compound). substances in a mixture have not combined chemically.

Sub-Atomic particles

Protons,neutrons,electrons

Atomic number (proton number)

Number of protons in the nucleus of an atom.

Mass number

Describes the number of particles in the nucleus (total number of protons and neutrons).

isotope

atoms of the same element with the same number of protons and electrons but different numbers of neutrons.

Electronic configuration

Arrangement of electrons in an atom. 2,8,8,16

Group

A column (vertical) on the periodic table. indicates the amount of valance (outer shell) electrons.

Period

A row (horizontal) on the period table. Indicates the amount of shells in an atom.

Cations

Positive ions

anions

Negative ions

ion

an atom or molecule that carries a net electrical charge due to the loss or gain of electron.

ionic bond

type of chemical bond formed through the electrostatic attraction between oppositely charged ions, resulting from the transfer of electrons from one atom to another.

Properties of ionic compounds

• High melting and boiling points.

• good electrical conductivity when in an aqueous solution or when molten, and poor when solid.

• Generally soluble in water (they dissolve to form solutions).

Giant lattice

a large-scale, repeating arrangement of ions or atoms in a three-dimensional structure, commonly found in ionic and covalent compounds.

Covalent bond

Formed when a pair of electrons is shared between two atoms leading to noble gas electronic configurations.

Properties of covalent compounds

• Low Melting and Boiling Points

• Many covalent compounds exist as gases or liquids at room temperature due to weak intermoleculair attractions.

• Soft or Brittle Solids.

Giant covalent structures

Consists of atoms linked together in a repeating three-dimensional lattice, forming a single, enormous structure rather than discrete molecules.

Properties of giant covalent structures.

• Strong covalent bonds throughout

• High melting and boiling points

• Hardness and strength

• Most giant covalent structures do not conduct electricity because there are no free electrons; exceptions include graphite and graphene, which have delocalized electrons that allow conductivity.

• generally insoluble in water and other solvents because the covalent bonds are too strong to be broken by solvent molecules.

Metallic bonding

The electrostatic attraction between positive metal ions and de-localised electrons.

Conductor

a material that allows electric current or heat to flow through it easily.