1. Atoms
Physical Science BHHS 2010/Melmore

2. Learning Objectives
Learning Objectives
Apply an understanding of the structure of the atom. Be able to interpret numbers of subatomic particles making up each atom.

3. Atomic Models
This model of the atom may look familiar to you. This is the Bohr model. In this model, the nucleus is orbited by electrons, which are in different energy levels.
A model uses familiar ideas to explain unfamiliar facts observed in nature.
A model can be changed as new information is collected.

5. ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ ve charge 1
neutron
No charge 1
electron
-ve charge
nil

6. Atoms are the smallest particles of an element that retains the chemical properties of that element
Parts:
Nucleus – small region in the center of the atom.
(+ charged protons, = charged neutrons)
Electron Cloud – large region, compared to nucleus, where electrons are found.

7. Size of nucleus vs. electron cloud
If an atom was the size of a sports stadium, the nucleus would be the size of a marble!
Subatomic Particles:
Protons : + charge, relative mass = atomic mass units (amu); round to 1
Neutrons: = charge, relative mass = atomic mass units (amu); round to 1
Electrons: - charge, relative mass = atomic mass units (amu); round to 0 (not factored in when figuring total mass of an atom)

8. Isotopes
Atoms with the same number of protons & electrons but a different number of neutrons.
They are the same element, but have different masses.
All isotopes are used to calculate atomic mass (reason why weight is a decimal).
Most elements consist of a mixture of isotopes.

9. Atomic Number
Number of protons in the nucleus (also the number of electrons)
Typically the number on top of the symbol on the Periodic Table. 13
Atomic Number
26.981

10. Mass Number Number of protons + number of neutrons in an atom.
When solving for number of neutrons: round mass number properly, subtract atomic number from mass number.

11. Mass Number
Mass number is the number of protons and neutrons in the nucleus of an isotope:
Mass # = p+ + n0
Nuclide p+ n0 e-
Mass #
Oxygen - 10 - 33 42
- 31 15 18 8 8 18
Arsenic 75 33 75
Phosphorus 16 15 31

12. Complete Symbols
Contain the symbol of the element, the mass number and the atomic number. X
Superscript →
Atomic
number
Subscript →
Mass
number

13. number of electrons = number of protons
ATOMIC STRUCTURE He 2
Atomic number
the number of protons in an atom 4
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons

14. Modern Atomic Structure electrons move so fast they look like a cloud and difficult to pinpoint

16. ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells around the nucleus of an atom.
first shell a maximum of 2 electrons
second shell a maximum of 8 electrons
third shell a maximum of 8 electrons

17. Electrons are in energy levels
Shells s p d f g
Total 1 2 6 8 3 10 18 4 14 32

19. N DOT & CROSS DIAGRAMS Nitrogen
With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X
Nitrogen N 7 X X N X X 14 X X

20. ELECTRONIC CONFIGURATION
With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example;
Nitrogen
configuration = 2 , 5 7
2 in 1st shell
5 in 2nd shell N
= 7 14

21. N DOT & CROSS DIAGRAMS Nitrogen
With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; X
Nitrogen N 7 X X N X X 14 X X

22. DOT & CROSS DIAGRAMS O Cl
Draw the Dot & Cross diagrams for the following elements; X 8 17 X O Cl a) b) X 35 X 16 X X X X X Cl X X X X X X X O X X X X X X X X X X

23. Pop QUIZ How many protons does Helium have
How many electrons does Zinc have
3. Silver has ____electrons
4. Magnesium____electrons
5. Uranium____electrons
6. Kryption ______protons
7. Aluminium____electrons
8. Bromine ____mass
9. Calcium ____electrons
10. Sodium has ______protons

24. ATOMIC QUIZ 2: Written answers
What is meant when an atom is said to be in its ground state?
3. The subatomic particle(s) found in the nucleus of an atom are
5. What is the maximum number of electrons that can occupy an atomic orbital?
8. In which way do isotopes of an element differ?
9. Calcium's atomic number is 20. What does that that tell us about a calcium atom?
10. What is ALWAYS true regarding atoms of two different elements?

25. Answers
1. What is meant when an atom is said to be in its ground state? CORRECT: The state an atom is found naturally.
3. The subatomic particle(s) found in the nucleus of an atom are
CORRECT: protons and neutrons.
5. What is the maximum number of electrons that can occupy an atomic orbital?
CORRECT: 2, 6, 10, 14
8. In which way do isotopes of an element differ?
CORRECT: number of neutrons in the atom
9. Calcium's atomic number is 20. What does that that tell us about a calcium atom?
CORRECT: It has 20 protons.
10. What is ALWAYS true regarding atoms of two different elements?
CORRECT: They have different numbers of protons.

26. ELECTRONIC CONFIGURATION
Write the electronic configuration for the following elements; 20 11 8 Na O Ca a) b) c) 16 23 40
2,8,8,2
2,8,1
2,6 17 14 5 Cl Si B d) e) f) 11 35 28
2,8,7
2,8,4
2,3

27. ELECTRONIC CONFIGURATION
Write the name, electronic configuration and diagram for the following elements; 4 12 Ca 20 Be Mg 2) 3) 1) 40 8 24
2,8,2
2,8,8,2
2,2 6 14 32 Ge 4) C 5) Si 6) 72 12 28
2,4
2,8,4
2,8,18,4 31 5 Ga 13 B 7) 8) Al 9) 10 69 26
2,8,18,3
2,8,3
2,3 35 F 9 17 Br
10)
11) Cl
12) 18 79 34
2,7
2,8,7
2,8,18,7

28. DO YOU REMEMBER ? The Atomic Number of an atom is the............
The Atomic Mass of an atom is
Protons in the nucleus equals the.....
The number of Electrons =
Electrons orbit the nucleus in _______
= number of protons in the nucleus.
= number of Protons + Neutrons in the nucleus.
= Number of Electrons.
Number of Protons
shells.

29. Structure of Subatomic Particles
Subatomic particles composed of fast moving points of energy called quarks
Quark Calculations (for protons and neutrons)
Each proton is 2 up quarks and 1 down quark
2(2/3) – 1(1/3) = 4/3 – 1/3 = 3/3 or +1
Each neutron is 2 down quarks and 1 up quark
2(-1/3) + 2/3 = 0
Each electron is composed of 2 down quarks
3(-1/3) = -1