Subatomic Particles

Electron

JJ Thomson discovered the electron using cathode ray experiment

Electron – smallest particle in an atom

Negatively charged

Directly involved in chemical reactions

Hangs out in the Electron Cloud

Electron Cloud – area around the nucleus where the electrons exist; mostly empty space; denser in areas where electrons are likely to exist

Ion – An atom that gains or loses electrons

Nucleus

Rutherford & the Gold Foil Experiment

Discovered the nucleus

Nucleus – densely packed group of protons and neutrons in the center

of the atom

Very tiny compared to whole atom

Electron cloud occupies most of the volume of the atom

Nucleus – Protons & Neutrons

Within the nucleus:

Proton - positively charged subatomic particle

Very heavy compared to the electron

Located in the nucleus

Neutron – neutral subatomic particle

About the same mass as a proton

Adds mass and stability to the nucleus

Discovered by Chadwick

Relative Masses

Particle Symbol Charge Relative Mass Actual Mass

Electron e- 1- 1/1840 9.11 x 10-28

Proton p+ 1+ 1 1.67 x 10-24

Neutron n0 0 1 1.67 x 10-24

The Atom

Atomic Number

Atomic Number - number on the periodic table; gives the number of

protons in the nucleus of the atom

# Protons = Atomic Number

# Protons = # Electrons (in a neutral element)

Carbon – Atomic Number = 6 : 6 protons in the nucleus

Barium – Atomic Number = 56 : 56 protons in the nucleus

Neutrons & Mass Number

Mass Number – the total number of protons and neutrons in an atom.

Shorthand notation:

Mass # = # Neutrons + # Protons

# Neutrons = Mass # - Atomic # (# Protons)

Atomic Number

Mass Number

Element Symbol

Neutrons

Find the number of neutrons using the atomic number and mass number.

Element Atomic Number Mass Number Neutrons

Beryllium (Be) 4 9

Neon (Ne) 10 20

Sodium (Na) 11 23

Isotope

Isotope – An atom that gains or loses a neutron.

Same number of protons, but different numbers of neutrons

Different neutrons = different masses

Same chemical, just a different mass

Neon-20 – 10 protons, 10 neutrons, 10 electrons

Neon-21 – 10 protons, 11 neutrons, 10 electrons

Neon-22 – 10 protons, 12 neutrons, 10 electrons

Atomic Mass

AMU – Atomic Mass Unit

Unit used for measuring the mass of an atom

Atomic Mass Number – weighted average mass of the atoms in a naturally occurring sample of the element.

Masses on the periodic table are decimals because they are an AVERAGE of the abundances of the isotopes.

Cl-35: 75%

Cl-37: 25%

Chlorine on the periodic table: 35.4527g/mol

Practice

Atomic Number Mass NumberNumber of

Protons

Number of

Neutrons

Number of

Electrons

Symbol of

Element

4 10

25 12

137 56

13 15