Review grade 9 chemistry

Periodic TableStructure of the Atom

Review of Grade 9 Chemistry

Quiz: Element Symbols first 20 elements plus Br and I transition metals: Sb, As, Bi, Cd,

Cr, Co, Cu, Au, Fe, Pb, Mn, Hg, Ni, Pt, Ag, Sn, Ti, Zn

Element symbol

Rules for writing the element symbols: First letter capitalize Second lower case

Hints to remembering symbols for elements: Hint 1: applies to hydrogen, boron, carbon, nitrogen,

oxygen, fluorine, phosphorus, sulfur, iodine etc. Hint 2: applies to helium, lithium, beryllium, neon,

aluminum, silicon, argon, calcium, bromine etc. Hint 3: applies to magnesium, chlorine, chromium,

manganese, zinc, cadmium, platinum etc. Hint 4: applies to sodium, potassium, iron, copper, silver,

tin, antimony, gold, mercury etc.

Periodic Table Periods: horizontal rows Families or Groups: vertical columns Elements in the same family have similar

physical and chemical properties

Periodic Table

Metals

left and centre of the periodic table

Transition elements (group 3-12)

Inner Transition elements (period 6 & 7)

Properties of Metals

conduct heat and electricity ductile and malleable Shiny, often silvery-grey in colour solid at room temperature (except mercury)

Non-Metals

right side of the periodic table

Properties of Nonmetals

poor conductors of heat and electricity usually solid or gas at room temperature

(only Bromine is a liquid at room temperature)

brittle dull

Metalloids Metals are separated from

non-metals by a staircase of elements called metalloids

Properties of Metalloids

properties intermediate between metals and non-metals

silicon tellurium

Chemical Families

Chemical Families

Alkali Metals (Group 1) soft, silver-grey metals reacts easily with water

Alkaline Earth Metals (Group 2) silver-grey metals harder and less reactive than

group 1 metals

Chemical Families

Halogens (Group 17) coloured non-metals very reactive

Noble Gases (Group 18) colourless non-metals odourless very unreactive (does not combine

easily with other atoms)

Atom

An atom is the smallest part of an element that has all the element’s properties

Atomic Theory

Each element has its own unique kind of atom Atoms of different elements vary in mass,

volume and reactivity

Atomic Theory

Atoms are not the smallest particles of matter Subatomic particles combine together

to form atoms Protons Neutrons Electrons

Subatomic Particles

Protons have a charge of 1+ Electrons have a charge of 1- Neutrons have a charge of 0 (neutral)

The masses of protons and neutrons are almost 2000 times greater than the mass of electrons

Subatomic Particle Summary

Particle Charge Relative Mass Location Influences…

Proton

Neutron

Electron



Proton +

Neutron 0

Electron -



Proton + 1

Neutron 0 1

Electron - 1/2000

Inside an Atom: Nucleus

Protons and neutrons form the core of an atom, called the nucleus

The protons and neutrons are held together by strong forces

Atomic Number

The number of protons in an atom is known as its atomic number

Each atom has a unique number of protons and thus each atom has a different atomic number

Mass Number

Together the protons and neutrons make up the mass of the atom

The mass number is the sum of the number of protons and neutrons in an atom

Inside an Atom: Electron Cloud

Surrounding the nucleus are a series of cloud-like energy levels called shells or orbitals

These shells are occupied by electrons

The electron cloud is 10,000 times larger than the nucleus

Inside an Atom

Imagine the nucleus to be the size of a golf ball. Then on this scale the first electron shell would be about one kilometer from the golf ball, the second shell about four kilometers, the third nine kilometers etc.



Proton + 1

Neutron 0 1

Electron - 1/2000



Proton + 1 Nucleus

Neutron 0 1 Nucleus

Electron - 1/2000 Shell

Inside an Atom: Charge

When the number of electrons equal the number of protons, the atom is neutral (no charge)

When there are more electrons (-) than protons (+) the charge is negative

When there are less electrons (-) than protons (+) the charge is positive



Proton + 1 Nucleus

Neutron 0 1 Nucleus

Electron - 1/2000 Shell



Proton + 1 Nucleus Mass &Charge

Neutron 0 1 Nucleus Mass

Electron - 1/2000 Shell Charge

Bohr Model of the atom

electrons surround the nucleus in shells (or orbital)

each shell has a specific energy level the innermost shell holds 2 electrons the next two shells hold 8 electrons the outermost shell is called the

valence shell

Bohr Model of the atom

the electrons in the valence shell are called valence electrons

Bohr diagrams

a Bohr diagram is an illustration of an atom that shows the arrangement and number of electrons in each shell

N7p7n

S16p16n

Cl17p18n

Let’s look at an example…

Example: Sulphur

Gather information from the periodic table to draw the Bohr diagram

Atomic number= number of protons= number of electrons (in a NEUTRAL atom)= 16

sulfur

16

S32.065

atomic number

atomic mass

Rules for drawing Bohr diagrams Place the symbol of the element in the center Electrons are drawn as far away as possible

(e.g. north-south, east-west orientations) Electrons pair up if there are more than 4 Keep count of the maximum number of

electrons per shell (first shell holds 2 electrons, the next two shells hold 8 each)

S

Example: Sulphur

Bohr diagram:first shell:2 electrons

second shell:8 electrons

third shell:6 electrons

total:16 electrons

Atomic number = 16

In a sulphur atom, the valence shell has 6 electrons

What’s wrong with this drawing?

The placement of electrons in the valence shell of this diagram is inaccurate

Electrons need to be as far away as possible.

What’s wrong with this drawing?

The placement of electrons in the valence shell of this diagram is inaccurate

Premature pairing of electrons

S

Create Bohr diagrams for the first 20 elements

1

3 4

11 12

19 20

2

5 6 7 8 9 10

13 14 15 16 17 18

Lewis dot diagrams

A drawing of an atom with ONLY it’s valence electrons

Example: Carbon

Example: Phosphorus

C

P

Lewis dot diagrams

If an atom has a full valence shell, no electrons are needed and thus only the element symbol is used

Example: Helium = He

Create Lewis dot diagrams for the first 20 elements

1

3 4

11 12

19 20

2

5 6 7 8 9 10

13 14 15 16 17 18

Trends in the Periodic Table

What trends do you see in the number of valence electrons for each group?


All atoms of elements in the same group have the same number of valence electrons

As the group number increases, so do the number of valence electron

Group 1 elements have 1 valence electron

Group 17 elements has 7 valence electron


What trends do you see in the number of orbitals for each period?


All atoms of elements in the same periodhave the same number of shells (orbitals)

As the period number increases, so do the number of shells

Period 2 elements have 2 orbitals

Period 3 elements have 3 orbitals

Counting Atoms Terms

Terms Definition Affect on atom count

Subscript Small number written to the lower right corner after the element symbol.

Indicates number of atoms of that element. If there are no numbers, a ‘1’ is assumed.

Brackets Surrounds a group of atoms. Used when there is more than one of a group of atoms (e.g. polyatomics)

All elements inside a bracket is in multiplies of the subscript written after the bracket.

Coefficient Large number written in front of a molecule.

Indicates the total number of the molecule. All elements after it would be in multiples of the number.


Terms Example Atom count

Subscript Na3PO4

Brackets Mg3(PO4)2

Coefficient 2 H2O

3 Mg3(PO4)2


Terms Example Atom count

Subscript Na3PO4 Na = 3P = 1O = 4

Brackets Mg3(PO4)2 Mg = 3P = 1 x 2 = 2O = 4 x 2 = 8

Coefficient 2 H2O H = 2 x 2 = 4O = 1 x 2 = 2

3 Mg3(PO4)2 Mg = 3 x 3 = 9P = 1 x 2 x 3 = 6O = 4 x 2 x 3 = 24

Review grade 9 chemistry

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