1. Atomic Structure

2. What is an atom?
Atom: the smallest unit of matter that retains the identity of the substance
First proposed by Democratus

3. Atomic Structure Atoms are composed of 2 regions:
Nucleus: the center of the atom
Accounts for the atomic mass of the atom
Electron cloud: surrounds the nucleus
Accounts for majority of the space in an atom
Nucleus
Electron
Cloud

4. Subatomic Particles The atom is composed of 3 subatomic particles:
1) Protons (positive) p+
2) Electrons (negative) e-
3) Neutrons (neutral) n

5. What’s in the Nucleus?
Both protons and neutrons are found in the nucleus
Neutrons
Protons

6. What’s in the Electron Cloud?
Electrons are found orbiting the nucleus in the electron energy shells (n)
Electrons

7. How is the overall change of an atom zero (neutral)?
This is because the # of protons = the # of electrons
Protons = Electrons
Example:
Protons = +20
Electrons = -20
Overall charge = 0

8. How do we know the number of subatomic particles in an atom?
Atomic number = number of protons
Ex: Hydrogen’s atomic number is 1
So hydrogen has 1 proton
Ex: Carbon’s atomic number is 6
So carbon has 6 protons
**The number of protons identifies the atom.
Example: 2 protons = Helium (He)
29 protons = Copper (Cu)

9. Learning Check #1 Identify the element using the number of protons given
A) Protons = 20
Calcium (Ca)
B) Protons = 56
Barium (Ba)
C) Protons = 53
Iodine (I)

10. How do we know the number of subatomic particles in an atom?
Mass number: protons + neutrons found in the nucleus of an atom
Mass # - Atomic # = # of neutrons
Example: Sodium (Na)
Mass # = 23 Protons = 11
= 12 neutrons

11. Learning Check #2 Find the number of neutrons in the following using the Mass # equation
A) Lithium (Li) 3 3
Atomic #= _______ = _______protons 7
Mass # = _______ 4
7 – 3 = 4 neutrons
# Neutrons = ______
B) Neon (Ne) 10 10
Atomic # = ______ = ______ protons
Mass # = ________ 20
20 – 10 = 10 neutrons
# Neutrons = ______ 10

12. What about the electrons?
The electrons are equal the protons
atomic # = protons = electrons
Example: Helium (He)
atomic # = 2
mass # = 4
p+ = 2
4 – 2 = 2 neutrons
e- = 2
n = 2

13. Learning Check #3 Determine the number of subatomic particles in the following:
A) Chlorine (Cl)
Atomic # = ____ 17
Mass # = _____ 35
p+ = ____
35 – 17 = 18 neutrons
e- = ____
n = ____ 18
B) Potassium (K)
Atomic # = _____ 19
Mass # = _____ 39
p+ = ____
39 – 19 = 20 neutrons
e- = ____
n = ____ 20

14. Bohr Model of the Atom Example: Neon (Ne) Atomic # = 10 Mass # = 20
20 – 10 = 10 neutrons
Atomic # = 10
Mass # = 20
Nucleus = all protons and neutrons
n3 = 18 e-
n1 = 2 e-
n4 = 32 e-
n2 = 8 e- 10 10 10
p+ = _____
e- = _____
n = _____

15. n1 is full. Must put the remaining 4 electrons in n2
Learning Check #4 Place the electrons in the correct energy shells on the Bohr Model below for Carbon (C) Find number of protons, electrons and neutrons first
mass # = __ atomic # = ___ 6 12
2 e- in n1
6 p+ and 6 n in the nucleus
n1 is full. Must put the remaining 4 electrons in n2
4 e- in n2
12 – 6 = 6 neutrons
p+ = ___ 6
e- = ___ 6
n = __

16. Mass # Atomic # Symbols Hyphen notation: carbon - 12 (mass #)
Show the Symbol of the element, Atomic number, & Mass number
Mass #
Atomic #
Hyphen notation: carbon - 12 (mass #)

17. Isotopes
Atoms with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers
Isotopes of Chlorine
35 Cl 37 Cl
Chlorine Chlorine - 37

18. Isotopes
Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons.
Neon-20, neon-21, and neon-22 are three isotopes of neon, a gaseous element used in lighted signs. Comparing and Contrasting How are these isotopes different? How are they similar?

19. Isotopes Isotope Protons Electrons Neutrons Nucleus Hydrogen–1
(protium) 1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium) 2

20. Average Atomic Mass
To calculate the average atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

21. Atomic Mass + Atomic Mass = + ….. (Mass isotope # 1) (% Abundance)

22. Rubidium has two common isotopes, 85Rb and 87Rb
Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is 72.2% and the abundance of 87Rb is 27.8%, what is the average atomic mass of rubidium?