Chapter Three

Law of Mendeleev

Properties of the elements recur in regular cycles (periodically) when the elements are arranged in order of increasing atomic mass

Atomic Mass

The actual mass of an atom (amu)

Daltons Atomic Theory

1. All matter is made of up of atoms (small, indivisible, indestructible fundamental particles) 2. Atoms can neither be created not destroyed (they persist unchanged for all eternity) 3. Atoms of a particular element are alike (in size, mass and properties) 4. Atoms of different elements are different from one another (different sizes, masses and properties) 5. A chemical reaction involves either the union or the separation of individual atoms.

Ion

An atom in which this electron-proton balance is not maintained has a net charge. You can only create an ion by adding or removing electrons from a neutral atom.

Why is an atom electrically neutral?

An atom is electrically neutral because the number of negatively charged electrons outside the nucleus equals the number of positively charged protons inside the nucleus.

Proton

Heavier subatomic particle present in all atoms. Positive electrical charge equal in magnitude but opposite in sign to that of the electron.

Percent by Mass is

Mass of element in compound/ Total mass of compound*100

Law of Constant Composition

Multiple samples of any pure chemical compound always contain the same percent by mass of each element making up the compound.

Periodic Table

Organised by Mendeleev Each vertical column is called a group Each horizontal row is called a period

Neutron

Same mass of Proton, subatomic particle, electrically neutral

Atomic Number

The number of protons in the nucleus of an atom. It alone determines the identity of the atom.

Law of Conservation of matter

When a chemical reaction takes place matter is neither created nor destroyed

Isotopes

different versions of the same element (# of neutrons)

Electrons

light and small subatomic particle, negative electrical charge, orbit the nucleolus. Electrons can't leave the atom without energy. They are attracted to the nucleus and so are kept from wandering away.

First Ionisation Energy

minimum amount of energy it takes to completely remove an electron from a neutral atom, forming a cation with a +1 charge

Anions

negatively charged ions (add electrons)

Cations

positively charged ions (lose electrons)

Mass number

the number of protons plus the number of neutrons in its nucleus