1. Unit 2 Chemistry and Radioactivity
Chapter 4: Atomic theory explains the formation of compounds

2. Chemistry Learning Outcomes
Differentiate between atoms, ions and molecules using knowledge of their structure and components.
Classify substances as acids, bases or salts based on their characteristics, name and formula.
Distinguish between organic and inorganic compounds.
Analyze chemical reactions, including reference to conservation of mass and rate of reaction.
Explain radioactivity using modern atomic theory.

3. Words to Know: Chapter 4.1 Atomic Theory and Bonding,
pages of BC Science 10 Textbook
Words to Know:
atomic number Bohr diagram
compound covalent bonding
ionic bonding ions
Lewis diagram molecule
valence electrons

4. What is an Atom?
The smallest particle of an element that still has the properties of that element
Fun Fact:
50 million atoms, lined up end-to-end = 1 cm
How small is an atom?
An atom = proton(s) + electron(s) + neutron(s) (PEN)

5. How small is an atom?

6. Pure Substances:
Are substances that are made of only one kind of matter.
Eg. Iron , Oxygen, Hydrogen 1

7. Pure Substances can be classified as either:
ELEMENTs – pure substance that cannot be chemically broken down into simple substances
are made up of one type of atom
Eg. oxygen,
Eg. hydrogen
2. COMPOUNDS – pure substances made up of more than one type of atom that are chemically combined.
eg. H2O is a compound

8. Physical Change
Is a change when the substance retains its original properties.
Eg. a cut strawberry is still as sweet
1. Change in shape – bending, cutting
2. Dissolving: when salt dissolves in water, the crystals disappear but the salty taste of water proves that the salt is still there. The salt can be re-crystallized by evaporating the water.
3. Change of state (phase change): water boiling to steam

9. Chemical Change:
occurs when the arrangement of atoms in compounds change, resulting in a new compound being formed.
The change is irreversible
Evidence of a new substance:
Gas produced (bubbles)
New change in colour, odour
Energy (heat or light) release or absorbed
Evidence of a chemical change: new substance created indicated by change in smell, color, temperature, production of a gas.

10. Structure of an Atom: The nucleus is at the centre of an atom
protons (positive charge) and neutrons (neutral charge), both found in the nucleus
Electrons (negative charge) exist in the space surrounding the nucleus

11. Subatomic particles have mass

12. Atomic number = # protons Atomic Mass = protons + neutrons

13. Where does most of the atom’s mass exist?
Nucleus (protons and neutrons)

14. What makes up most of the atom’s volume?
electrons

15. Question What determines the nuclear charge?
Protons – bc neutrons are neutron and electrons are outside

16. Question Which particles determine the atomic number?
Protons and electrons

17. Question Which particles determine the atomic number?
Protons (or electrons)
Protons and electrons

18. Numbers to Remember : Atoms are neutral, therefore:
# of protons = # of electrons in every atom
AND ONLY IN ATOMS!!! (not ions)
Nuclear charge = charge on the nucleus = # of protons
Atomic number = # of protons
= # of electrons
Why does nuclear change only depend on protons? Electrons are outside and neutrons are neutroal

19. Does atomic mass always equal atomic number?

20. Is atomic mass always twice the atomic number?
Does atomic mass always equal atomic number?

21. Homework
Read pages
Answer Check your Understanding: p #1-3, 5-9, 10f, 11
Read pages in text book

23. Video Crash Course periodic table:
Crash Course periodic table:

24. The Periodic Table: The periodic table organizes the elements by
atomic number
There are 3 types of elements:
metals are on the left
non-metals are on the right
metalloids form a “staircase” in the middle.
Rows of elements (across) are called periods
Columns (vertical) are called groups/families

25. Families of the Periodic Table:
All elements in a family have…
similar properties
bond with other elements in similar ways
have the same number of valence electrons
Family names:
Group 1 = alkali metals (sodium)
Group 2 = alkaline earth metals (calcium)
Group 17 = the halogens (chlorine)
Group 18 = noble gases (neon)
First column (Group 1) of Periodic Table (but does not include Hydrogen.
They all have one electron in their outer shell.
Metallic elements that are shiny, soft and have low densities.
Malleable (bendable), some soft enough can be cut with a knife
Not found freely in nature because they all react vigorously with oxygen and water
Second most reactive family
When mixed in solution they are likely to form “basic” or “alkaline” solutions.
2 electrons in valence shell

26. Group I: Alkali Metals does not include Hydrogen.
all have one electron in their outer shell.
Metallic elements that are shiny, soft and have low densities.
Malleable (bendable), some soft enough can be cut with a knife
Not found freely in nature because they all react vigorously with oxygen and water

27. Group II: Alkali Earth Metals
Second most reactive family
When mixed in solution they are likely to form “basic” or “alkaline” solutions.
2 electrons in valence shell

28. Group XVII: Halogens Non-metals seven electrons in their outer shell
very reactive
Greek words meaning “forming salts.”
Fluorine most reactive.
halogens are often used to kill harmful microorganisms. For example, the halogen chlorine is used to prevent the growth of algae in swimming pools and to purify drinking water. Solutions containing iodine are often used in hospitals and in doctors’ offices to kill germs on skin.

29. Group XVIII: Nobel Gases
Have eight electrons in their outermost orbitals.
Inert (non-reactive)
The noble gases and helium are all "happy," because their valence shell is full. 
Helium (He) is different from all of the other elements. It is very stable with only two electrons in its outer orbital (valence shell). Even though it only has two, it is still grouped with the noble gases

30. Where are the following?
INCREASING REACTIVITY
Where are the following?
Atomic Number
Period
Group/Family
Metals
Non-metals
Transition metals
Metalloids
Alkali metals
Alkaline earth metals
Halogens
Noble gases
rows of elements called periods.
vertical columns of elements are called groups, or families.

31. Bohr Diagrams
Show the arrangement of subatomic particles in atoms and ions.
Electrons arranged in energy levels called shells.
First shell contains 2 electrons,
then 8, 8, 18, 18.
Outermost shell is called valence shell.
Stable octet is when the valence shell has 8 electrons.

32. Bohr Diagram

33. What patterns do you notice?
Within a row?
Within a family?
What patterns do you notice (period row – shell, and group/columne and valence e)

34. What patterns do you notice (period row – shell, and group/columne and valence e)
Note: The noble gas elements have full electron shells, and are very stable.

35. Row determines # shells
Except for the transition elements,

36. Group number (column) determines the number of valence electrons

37. Bohr Diagrams: Practice
What element is this?
It has = 18 electrons, and therefore 18 protons
It has 3 electron shells, so it is in period 3
It has 8 electrons in the outer (valence) shell
18 p
22 n
Argon

38. Ions
It is more stable to achieve a full valence shell (like the noble gases). To do this, atoms will either lose or gain electrons to become ions (electrically charged particles)

39. What does sodium need to do to become more like a noble gas? Chlorine?
Note: The noble gas elements have full electron shells, and are very stable.
What does sodium need to do to become more like a noble gas?
Chlorine?
Note: The noble gas elements have full electron shells, and are very stable.
What does sodium need to do to become more like a noble gas? Chlorine?

40. Bohr Model of an Ion
Remember, an ion is an atom that has gained a charge (by either losing or gaining one or more electrons)
The Bohr model indicates the charge with a “+ or –” and brackets.
Note

41. Bohr model of ions Sodium atom Sodium ion
Sodium ion has lost it’s outer most electron (-) to become more stable (like the noble gases) and now has a positive charge, indicated by the + and brackets.

42. Practice: Draw the Bohr model diagram for an aluminium atom and ion.
aluminum-27 atom: aluminium-27 ion:

43. Draw the Bohr model diagram for an aluminium atom and ion.
aluminum-27 atom: aluminium-27 ion:

44. Periodic Table and Ion Formation:
Elements on the Left of the Periodic Table (metals) lose electrons and become positive ions (called cations)
Elements on the Right (Non-metals) tend to gain electrons and become negative ions (called anions)

45. Forming Compounds:
When two atoms get close together, their valence electrons interact.
If the valence electrons can combine to form a low-energy bond (to become more stable), a compound is formed.
Each atom in the compound attempts to have the stable number of valence electrons as the nearest noble gas.

46. Ionic Bonds:
Ionic bonds form when electrons are transferred from cations (+) to anions (-).
involves a metal (+) and a non-metal (-)
For example, lithium and oxygen form an ionic bond in the compound Li2O

47. Bohr Model of an Ion
The Bohr model indicates the charge with a “+ or –” and brackets.
Note

48. Bohr Model of Ionic bond
Bohr diagram of CaF2
Notice that each balance shell is full, making the element resemble the nearest noble gas

49. Bohr Model of Ionic Bond

50. Ionic Compounds
Ionic substances form structured lattices containing oppositely charged ions.
They have high melting and boiling points,
conduct electricity when melted or dissolved in water.
Eg NaCl. LiCa

51. Covalent Bonds: form when electrons are shared between two non-metals.
Electrons stay with their atom, but overlap with other shells

52. Covalent Bonds A covalent bond, also called a molecular bond
A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. 
Molecules are distinguished from ions by their lack of electrical charge.
The pair of electrons involved in the bond is called a bonding pair.

53. Covalent compounds Involve non-metals only.
Have lower melting points than ionic compounds (due to weaker bonds)
Do not conduct electricity when solid or dissolved (no ions)

54. Bohr Diagram of Covalent bonds
Because a covalent bond means electrons are shared, valence electrons overlap (spending time orbiting both elements)
indicated by shell from each element in the bond touching.

55. Bohr Diagram of Covalent bonds

56. Check your understanding
What types of elements form ionic bonds?
What is the main difference between ionic and covalent bonds?
Metal and non-metal
Electrons are lost/gained or shared.

58. Lewis Diagrams:
Invented by an American chemist Gilbert Lewis (1875 – 1946)
Demonstrates chemical bonds by only showing the valence electrons and symbol.
Example: Nitrogen atom

59. Lewis Diagrams:
Note: the Lewis diagrams are the same (except for the symbols) for elements in the same family because they have the same number of valence electrons

60. Rules for drawing Lewis Diagrams
Dots representing valence electrons are placed around the element symbol (on 4 sides, imagine a box around the symbol)
Dots are placed singly, until the fifth electron is reached, then they are paired.

61. Lewis Diagrams for Ions:
For positive ions: one electron dot is removed from the valence shell for each positive charge of the ion.
Because only valence electrons are shown in Lewis diagrams, the positive ion usually not have any valence electrons left to show.

62. Lewis Diagrams for Ions:
For negative ions: one electron dot is added to each valence shell for each negative charge of the ion.
Usually means the symbol is surrounded by all 8 dots.
Place Square brackets around each ion to indicate the proper charge.

63. Lewis Diagram for Ionic Compound

64. Lewis Diagrams For Covalent Bonds:
The shared pairs of electrons are usually drawn as a straight line
Like Bohr diagrams, valence electrons are drawn to show sharing of electrons.
All atoms “like” to have a full valence shell

65. Bonding pairs, lone pairs
Valence electrons involved in the bonding are called a bonding pair.
Valence electrons NOT involved in the bond are called lone pairs.

66. Lewis Diagram for Diatomic Molecules
Diatomic molecules are molecules composed of only two atoms. This makes them more stable than individual atoms.
of the same or different chemical elements. The prefix di- is of Greek origin, meaning "two". If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H2) or oxygen (O2), then it is said to be homonuclear.diatomic molecule: Diatomic molecules are molecules composed of only two atoms,

67. Oxygen forms a diatomic molecule

68. How would you draw a Lewis diagram for diatomic molecule of Nitrogen?

69. How would you draw a Lewis diagram for diatomic molecule of Nitrogen?