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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