chem unit 2

• Matter is composed of extremely small particles called atoms
• Atoms are indivisible and indestructible
• Atoms of a given element are identical in size, mass and chemical properties
• Atoms of a specific element are different from those of another element
• Different atoms combine in simple whole-number ratios to form compounds
• In a chemical reaction, atoms are separated, combines or rearranged

An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus.

• Negatively charged particles that are part of all forms of matter.
• Mass of an electron = 9.1 x 10-28g=1/1840

JJ Thomson's plum pudding model of an atom states that the atom is a uniform, positively charged sphere containing electrons,

in Rutherford's nuclear model, the atom is composed of dense, positively charged nucleus that is surrounded by negative electrons. Alpha particles passing far from the nucleus are only slightly deflected. Alpha particles directly approaching the nucleus are deflected at large angles

A subatomic particle carrying a charge equal to but opposite that of an electron.

It is a subatomic particle that has a mass nearly equal to that of a proton, but it carried no electric charge.

Atoms are composed of a nucleus containingprotons and neutrons, and surrounded by a cloud of electrons.

The number of protons in an atom (also number of electrons).

Is the sum of the atomic number (or number of protons) and neutrons in the nucleus.

Atoms with the same number of protons but different numbers of neutrons.