Atoms, Ions, and Isotopes

• All matter is composed of particles called atoms.

• An atom is the smallest unit of an element that carries the general properties of that element.

• Atoms are composed of subatomic particles.

• The three most important subatomic particles are protons, neutrons, and electrons.

Atoms, Ions, and Isotopes

• A proton is a subatomic particle that has a charge of +1.

• A proton is a subatomic particle that has a mass of ≈1 amu (amu = atomic mass unit).

• A proton can be symbolized two different ways!

letter symbol:

or

the mass-charge symbol: (the superscript = mass & the subscript = charge).

Atoms, Ions, and Isotopes

p

11H

• A neutron is a subatomic particle that has a charge of 0 (zero).

• A neutron is a subatomic particle that has a mass of ≈1 amu (In reality, a neutron is slightly more massive than a proton).

• A neutron can be symbolized two different ways!

letter symbol:

or

the mass-charge symbol: (the superscript = mass & the subscript = charge).

Atoms, Ions, and Isotopes

n

10n

• An electron is a subatomic particle that has a charge of -1.

• An electron is a subatomic particle that has a mass of ≈0 amu (In reality, an electron does have

a very very very very small mass).

• An electron can be symbolized two different ways!

letter symbol:

or

the mass-charge symbol: (the superscript = mass & the subscript = charge).

Atoms, Ions, and Isotopes

e-

0-1e

• The subatomic particles in order of increasing mass:

Ex. (1) Complete the following chart.

electron → proton → neutron.

Subatomic Particle

Mass ChargeLetter

SymbolMass Charge

Symbol

Proton

Neutron

Electron

Atoms, Ions, and Isotopes

1 amu

1 amu

0 amu

+1

0

-1

p

n

e-

11H

10n

0-1e

Ex. (2) Rank the subatomic particles from highest to lowest mass. ______ > ______ >

______ • An atom’s atomic number (symbolized by the

letter “Z”) is equal to its number of protons.

• An atom’s mass number (symbolized by the letter “A”) is equal to the sum of its number of protons and neutrons.

• Caution: mass number is not the same as atomic mass, which will be explained later.

mass number ≠ atomic mass

Atoms, Ions, and Isotopes

n p e-

• An ion is a charged atom or group of atoms.

• An ion composed of a single atom is called a monoatomic ion.

Na1+ Cu2+ Al3+ Cl1- O2- As3-

• An ion composed of two or more atoms is called a polyatomic ion (see Reference Table E).

NO31- NH4

1+ SO42- H3O1+ PO4

3-

Atoms, Ions, and Isotopes

• A positively charged ion (one that has more protons than electrons) is called a cation.

Na1+ Cu2+ Al3+ NH41+ H3O1+

• A negatively charged ion (one that has more electrons than protons) is called an anion.

Cl1- O2- As3- NO31- SO4

2- PO43-

• In a atom, the number of protons is equal to the number of electrons.

Atoms, Ions, and Isotopes

• Dalton proposed, in his atomic theory, that atoms of the same element were exactly the same.

• Isotopes of the same element exist because not all atoms of the same element are completely identical.

Atoms, Ions, and Isotopes

• Isotopes can be defined in several ways that actually say the same thing.

– Isotopes are two atoms of the same element that have different masses.

– Isotopes are two atoms that have the same atomic number but that have different mass numbers.

– Isotopes are two atoms that have the same number of protons but different numbers of neutrons.

Atoms, Ions, and Isotopes

• Isotopes are identified by their isotope number which is the same as the mass number (the number of protons and neutrons)!

Hydrogen-1 has 1 proton and 0 neutrons.

Hydrogen-2 has 1 proton and 1 neutron.

Carbon-12 has 6 protons and 6 neutrons.

Carbon-14 has 6 protons and 8 neutrons.

Atoms, Ions, and Isotopes

Ex. (1) K-39: #p = _____ and # n = _____

Ex. (2) Ni-59: #p = _____ and # n = _____

Ex. (3) N-14: #p = _____ and # n = _____

Ex. (4) 56 p and 81 n : _____-_____

Ex. (5) 14 p and 15 n : _____-_____

Ex. (6) 43 p and 56 n : _____-_____

Atoms, Ions, and Isotopes19 20

28 31

7 7

137Ba

Si

Tc

29

99