Atoms and isotopes

Radius of an atom

• very small

• 1 × 10^-10m

Basic structure of an atom

• a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons

• In an atom the number of electrons is equal to the number of protons in the nucleus

• All atoms of a particular element have the same number of protons. The number of protons in an atom of an element is called its atomic number

How much smaller is the radius of a nucleus than the radius of an atom?

The radius of a nucleus is less than 1/10 000 of the radius of an atom

Where is most of the mass in an atom concentrated?

in the nucleus

Where are the electrons in an atom?

• The electrons are arranged at different distances from the nucleus (different energy levels)

• The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level)

Relative charge of subatomic particles

• Proton = 1

• Electron = -1

• Neutron = 0

Why does an atom have no overall charge?

• total positive charge = total negative charge because number of protons = number of neutrons. Charges cancel each other out

• Neutrons are neutral

Relative mass of subatomic particles

• Proton = 1

• Electron = 1/2000 (close to 0)

• Neutron = 1

What is an isotope?

• atom with the same number of protons but a different number of neutrons

• Only one or two of an element’s isotopes are stable

What happens is an atom loses one or more outer electrons

becomes a positive ion