1. Unit 3 – Atoms, Ions, Isotopes

2. Conclusions from the Study of the Atom (so far…)
Atom – smallest particle of an element that retains the properties of the element.
Composed of 3 subatomic particles:
Electrons
Protons
neutrons

3. Conclusions from the Study of the Atom (continued)
Helium-4
Nucleus - small, dense center of an atom that contains nearly all of the atom’s mass
Most of the mass of the atom is in the nucleus
Most of the volume of the atom is empty space
Image: User Yzmo Wikimedia Commons.

4. amu: atomic mass unit. 1 amu = 1.67 x 10 g
Atomic Particles
Particle
Charge
Location
Mass (amu)
Mass (g)
Electron, e- -1
Electron cloud ~0
9.11 x 10–28
Proton, p+ +1
Nucleus 1
1.67 x 10–24
Neutron, n0
amu: atomic mass unit. 1 amu = 1.67 x 10 g

5. Protons and neutrons are made of quarks.
4.2
Protons and neutrons are made of quarks.
Electrons cannot be divided into smaller particles (as far as we know so far…..)

6. Identifying Atoms PROTONS determine the identity of the atom.
1 proton = Hydrogen
2 protons = Helium
6 protons = Carbon
ISOTOPES are atoms of the same element with different numbers of neutrons.
Carbon-12 has 6 protons + 6 neutrons
Carbon-13 has 6 protons + 7 neutrons

7. Isotopes
Isotopes are atoms of the same element with different numbers of neutrons.
Isotope
Protons
Electrons
Neutrons
Nucleus
Hydrogen–1
(protium) 1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium) 2

8. Atomic Number
Atomic number
Atomic number of an element is the number of protons in the nucleus of each atom of that element.
In a NEUTRAL atom, the atomic # is also the number of electrons.
Atom p+ n0 e-
Mass #
Oxygen 10 33 42 15 31 8 8
Arsenic 33
Phosphorus 15

9. Mass Number Mass # = p+ + n0
Mass number is the number of protons and neutrons in the nucleus of an isotope.
It is NOT on the periodic table.
Mass # = p+ + n0
Atom p+ n0 e-
Mass #
Oxygen 10 33 42 15 8 8 18
Arsenic 33 75
Phosphorus 16 15 31

10. Isotope Naming
HYPHEN NOTATION
Hydrogen-3
Element name and the mass number
NUCLEAR NOTATION
𝟑 𝑯 or 𝟏 𝟑 𝑯 Element symbol and mass number (top) and atomic number (bottom)

11. Isotopes - Naming
How would you write Uranium-235 using the symbol? (atomic number = 92)

12. The total number of protons
REVIEW:
Atomic Number:
The total number of protons
Atomic number = # protons = # electrons
Mass Number:
The total number of protons and neutrons in a specific atom
Mass number = # protons + # neutrons

13. Ions IONS - atoms that have gained or lost electrons
Charged particles because unequal number of p+ and e-
Metals lose electrons to form CATIONS (positively charged ions)
Non-metals gain electrons to form ANIONS (negatively charged ions)
A Negative ION

14. Practice
Find the number of protons, neutrons & electrons:
p+ n0 e-
23Na
16O2–
12C

15. Average Atomic Mass
All isotopes of an element do not exist in equal abundance in the world
Percent abundance in world:
90.48% % %

16. Atomic Mass Atomic Mass = weighted average of mass #’s of all isotopes
Atomic number
Atomic Mass = weighted average of mass #’s of all isotopes
(ON the periodic table)
Atomic mass
Atomic Mass= % abundance mass # + % abundance mass # +… 100
Atom
Mass #
Percent Abundance
Carbon-12 12
98.89
Carbon-13 13
1.11
Carbon-14 14
0.01
𝟗𝟖.𝟖𝟗 𝟏𝟐 + 𝟏.𝟏𝟏 𝟏𝟑 +(𝟎.𝟎𝟏)(𝟏𝟒) 𝟏𝟎𝟎 =𝟏𝟐.𝟎𝟏 amu

17. Neon-20 Neon-21 Neon-22 Calculate the average atomic mass of Neon 20.0
Example #1
Calculate the average atomic mass of Neon
Atomic Mass= % abundance mass # + % abundance mass # +… 100
Isotope
Mass (amu) (M)
Percent abundance (P)
Neon-20
20.0
90.48%
Neon-21
21.0
0.27%
Neon-22
22.0
9.25%
= 20.2 amu

18. Atomic Mass Neon-20 Which isotope is most abundant?
If Neon has 3 isotopes:
Neon-20, Neon-21, Neon-22,
Weighted average atomic mass is 20.2 amu.

19. Example #2
Calculate the average atomic mass of Lithium
Isotope
Mass (amu) (M)
Percent abundance (P)
Lithium-6
6.01
7.5%
Lithium-7
7.01
92.5%
= 6.94 amu

20. Cesium-132 Cesium-133 Cesium-134
Example #3
Calculate the average atomic mass of Cesium
Isotope
Mass (amu) (M)
Percent abundance (P)
Cesium-132
132.0
75.0%
Cesium-133
133.0
20.0%
Cesium-134
134.0
5.0%
= amu

21. Questions 1) What particles make up an atom?
Protons, Neutrons and Electrons
2) What are the charges on these particles?
Protons (+1), Neutrons (none), Electrons (-1)
3) What particles make up the nucleus?
Protons and Neutrons
3) What is the mass number?
Mass of a specific atom = # p+ + # n0

22. More Questions: Atomic Number tells us: Atomic Mass tells us:
The identity of the element; the number of protons (and electrons in a neutral atom)
Atomic Mass tells us:
The average mass in amu of all naturally occuring isotopes
Mass