1. The Structure of the Atom
CHAPTER 5
The Structure of the Atom
5.1 The Atom has a Structure

2. What we’ve seen so far… Chapter 1 The Science of Chemistry
- Chemistry is about discovering and understanding natural laws using the scientific method
- Energy cannot be created nor destroyed
Chapter 1
The Science of Chemistry

3. What we’ve seen so far… Chapter 1 Chapter 2 The Science of Chemistry
- Matter can be mixtures or substances. The smallest unit of a pure substance is an element.
- Each element is a type of atom, and they can be arranged in a periodic table.
- Atoms come together to form compounds. Atoms with an electric charge are known as ions.
Chapter 1
The Science of Chemistry
Chapter 2
Matter and Atoms

4. What we’ve seen so far… Chapter 1 Chapter 2 Chapter 3
The Science of Chemistry
Chapter 2
Matter and Atoms
Chapter 3
Temperature, Energy, and Heat
- Temperature is a measure of kinetic energy.
- Heat is thermal energy.
- Heat gain and heat loss can cause phase changes, as molecules are rearranged.

5. What we’ve seen so far… Chapter 1 Chapter 2 Chapter 3 Chapter 4
The Science of Chemistry
Chapter 2
Matter and Atoms
Chapter 3
Temperature, Energy, and Heat
Chapter 4
Physical and Chemical Change
- In a physical change molecules are rearranged. In a chemical change atoms are rearranged to make new substances.
- Chemical reactions can be endothermic or exothermic.
- Many reactions occur in aqueous solution, and some elements are more reactive than others.

6. How can we explain the properties and behaviors observed so far?
Chapter 1
The Science of Chemistry
Chapter 2
Matter and Atoms
Chapter 3
Temperature, Energy, and Heat
Chapter 4
Physical and Chemical Change
How can we explain the properties and behaviors observed so far?

7. Answers can be found inside the atom
Chapter 1
The Science of Chemistry
Chapter 2
Matter and Atoms
Chapter 3
Temperature, Energy, and Heat
Chapter 4
Physical and Chemical Change
How can we explain the properties and behaviors observed so far?

8. 92 different types of atoms!

9. Each of the elements is a unique type of atom.
Atoms are made from smaller particles!
protons
neutrons
electrons
Each of the elements is a unique type of atom.

10. How did scientists come up with this?
Atoms are made from smaller particles!
protons
neutrons
electrons
How did scientists come up with this?

11. It started a long time ago…
460 – 370 BC
Today
Democritus
Beginning of Atomism
You cannot divide something in half forever.
The smallest piece of matter is called an atom.

12. 1. All elements are made of tiny indivisible particles called atoms.
Dalton’s Postulates
460 – 370 BC
1808
Today
1. All elements are made of tiny indivisible particles called atoms.
Democritus
Atomism
Over 2,000 years later
John Dalton comes up with the first “modern” atomic theory.

13. 1. All elements are made of tiny indivisible particles called atoms.
Dalton’s Postulates
460 – 370 BC
1808
Today
1. All elements are made of tiny indivisible particles called atoms.
Democritus
Atomism
2. All atoms of the same element are the same, but different from atoms of every other element.
Over 2,000 years later
John Dalton comes up with the first “modern” atomic theory.

14. 1. All elements are made of tiny indivisible particles called atoms.
Dalton’s Postulates
460 – 370 BC
1808
Today
1. All elements are made of tiny indivisible particles called atoms.
Democritus
Atomism
2. All atoms of the same element are the same, but different from atoms of every other element.
Over 2,000 years later
John Dalton comes up with the first “modern” atomic theory.
3. Chemical reactions rearrange atoms but do not create, destroy, or convert atoms from one element to another.

15. 1. All elements are made of tiny indivisible particles called atoms.
Dalton’s Postulates
460 – 370 BC
1808
Today
1. All elements are made of tiny indivisible particles called atoms.
Democritus
Atomism
2. All atoms of the same element are the same, but different from atoms of every other element.
Over 2,000 years later
John Dalton comes up with the first “modern” atomic theory.
3. Chemical reactions rearrange atoms but do not create, destroy, or convert atoms from one element to another.
4. Compounds are made from combining atoms in simple whole number ratios.

16. Another kind of light?
460 – 370 BC
1808
1870
Today
Democritus
Atomism
Dalton
“Modern”
atomic theory
William Crookes invents a tube in which virtually all the gas has been removed.
Under high voltage, a ray was emitted from the cathode end of the tube.

17. Cathode rays must be negative.
It started a long time ago…
460 – 370 BC
1808
1870
1897
Today
Democritus
Atomism
Dalton
“Modern”
atomic theory
Crookes
Cathode rays
J.J. Thomson discovers the electron
Cathode rays must be negative.

18. It started a long time ago…
460 – 370 BC
1808
1870
1897
1910
Today
Democritus
Atomism
Dalton
“Modern”
atomic theory
Crookes
Cathode rays
Thomson
Discovery
of the electron
Ernest Rutherford discovers the nucleus

19. Size and mass
The size of the atom comes mostly from the space occupied by the electrons
The mass of the atom comes mostly from the nucleus

20. Charges in the atom
neutrons
protons
electrons

21. Charges in the atom
A complete atom has a charge of zero

22. Charges in the atom

23. What happens when you change the number of protons?
neutrons
protons
electrons
What happens when you change the number of protons?

24. You obtain a different element!
6 protons in carbon
7 protons in nitrogen
8 protons in oxygen
You obtain a different element!
The number of protons is also called the atomic number for that element.

25. What happens when you change the number of electrons?
neutrons
protons
electrons
What happens when you change the number of electrons?

26. Na Na1+ 11 protons A neutral sodium atom A positive sodium ion
The protons and
electrons cancel each other out
Balanced charges
A positive sodium ion
Na1+
One proton is not neutralized by an electron, making this a +1 charged atom
One electron short

27. O2- 8 protons A negative oxygen ion
Two electrons are not neutralized by protons, making this a –2 charged atom
Two extra electrons

28. The electron cloud Electrons are very light and fast.
They are not organized along orbits around the nucleus.
Except for mass, virtually every property of atoms is determined by electrons, including size and chemical bonding

29. What happens when you change the number of neutrons?
protons
electrons
What happens when you change the number of neutrons?

30. They hold protons together in the nucleus.
Atomic number
Neutrons act as “glue.”
They hold protons together in the nucleus.

31. 12C Mass number = 6 p + 6 n = 12 “carbon-12”
mass number: total number of protons and neutrons in a nucleus.

32. Name
Mass number
# protons
# neutrons

33. Carbon-12 Carbon-13 Carbon-14
Name
Mass number
# protons
# neutrons

34. Carbon-12 Carbon-13 Carbon-14
Name
Mass number
# protons
# neutrons

35. Carbon-12 Carbon-13 Carbon-14
Name
Mass number
# protons
# neutrons

36. Carbon-12 Carbon-13 Carbon-14
Name
Mass number
# protons
# neutrons

37. isotopes: atoms or elements that have the same number of protons in the nucleus but different number of neutrons.

38. How can lithium have 0.941 neutrons?
Two lithium isotopes in nature
Atomic mass
How can lithium have neutrons?

39. Number of neutrons for each of 100 lithium atoms randomly sampled from nature
It’s an AVERAGE mass!

40. Isotope periodic table (first 4 rows)

41. Radioactivity Lithium-8 is unstable and decays:
radioactivity: a process by which the nucleus of an atom spontaneously changes itself by emitting particles or energy.
decay: the process during which a nucleus undergoes spontaneous change.

42. There must be a force that keeps the nucleus together
Forces in the atom
There must be a force that keeps the nucleus together

43. Electrons form bonds between atoms.
Forces in the atom
In the nucleus
Electrons
The strong nuclear force attracts protons to protons, neutrons to neutrons, and protons to protons
Electrons repel each other, but don’t “fall into” the nucleus because they are in constant motion.
Electrons form bonds between atoms.

44. The size of the atom comes mostly from the electrons
460 – 370 BC
1808
1870
1897
1910
Today
Democritus
Atomism
Dalton
“Modern”
atomic theory
Crookes
Cathode rays
Thomson
Discovery
of the electron
Rutherford
Discovery
of the nucleus
electrons
protons
neutrons
The size of the atom comes mostly from the electrons
The mass of the atom comes mostly from the nucleus