Chemistry - Periodic Table of Elements

Element

A pure substance that cannot be broken down during normal physical and chemical changes.

Compound

Pure substance made up of two or more different elements that are chemically joined.

Metals

Solid at room temperature, shiny/lusture, good conductors of heat and electricity.

Non-metals

Mostly gases and solids at room temp, look like gasses or dull powders, poor conductors of heat and electricity.

Metalloids

Solids at room temp, look shiny or dull, may conduct electricity and poor conductors of heat.

Period

A horizontal row on the periodic table labelled from 1 to 7.

Group

A vertical column on the periodic table labelled from 1 to 18. Also known as chemical family.

Chemical Family

A column of elements with similar chemical and physical properties.

Chemical Family of Hydrogen

Belongs to a family of its own

Alkali Metals (Group 1) Highly reactive metals. Shiny silver and soft. Always combined with other elements in nature (eg. NaCl or sodium chloride).

Alkaline Earth Metals (Group 2)

Shiny and silvery. Not as soft or reactive as the alkali metals. Several of these elements are important mineral nutrients (Mg and Ca).

Halogens (Group 17)

Very reactive. Always found combined with another element in nature. Used as disinfectants and to strengthen teeth.

Noble Gases (Group 18)

Very unreactive, inert, gasses. Used in neon signs.

Transition Metals (group 3-12)

Less reactive, harder metals. Includes metals used in jewelry and construction. Metals used “as metal”.

Electron

Outside of nucleus. Particle symbol e− . Mass of near zero. Charge of -1

Proton

Inside of nucleus. Particle symbol p+. Mass nearly 2000x greater than electron. Charge of +1

Neutron

Inside of nucleus. Particle symbol n0. Mass nearly 2000x greater than electron. Charge of 0.

Atomic Number

The number of protons in the atom’s nucleus.

Atomic Mass

The weighted average masses of the isotopes of an element.

Isotope

An atom with the same number of protons but a different number of neutrons.

Mass number

The number of protons and neutrons in an atom’s nucleus.

Isotope Notation

Top left, mass number. Bottom left, atomic number. Right, element symbol.

Bohr-Rutherford Diagram for the first 20 elements

2 electrons in the first shell, 8 in the second, 8 in the third, and 2 in the fourth.

Elements in the same group in the periodic table have the same number of valence electrons (outer electrons).

Ions

Atom that have either gained or lost electrons and are no longer neutral. This is because when the valence shell of an atom is not full with 8 electrons, the atom is not stable. The atom is likely to lose orgain electrons (whichever is easiest).

Cations

Metals usually have 1, 2, or 3 valence electrons and tend to lose electrons, becoming cations (positive ions).

Anions

Non metals usually have 5, 6, or 7 valence electrons and tend to gain electrons, becoming anions (negative ions). The noble gases have full valence shells, therefore they are stable and do not gain or lose electrons.

Subscript

The number of atoms of the element.

Anatomy of a chemical formula

Left to right. Symbol of element, subscript, symbol of next element, subscript, etc.

Molecule

Has two or more atoms of the same or different elements that are chemically bonded together. Eg. oxygen gas O2 and carbon monoxide CO.