review grade 9 chemistry
TRANSCRIPT
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Periodic TableStructure of the Atom
Review of Grade 9 Chemistry
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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
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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.
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Periodic Table Periods: horizontal rows Families or Groups: vertical columns Elements in the same family have similar
physical and chemical properties
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Periodic Table
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Metals
left and centre of the periodic table
Transition elements (group 3-12)
Inner Transition elements (period 6 & 7)
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Properties of Metals
conduct heat and electricity ductile and malleable Shiny, often silvery-grey in colour solid at room temperature (except mercury)
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Non-Metals
right side of the periodic table
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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
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Metalloids Metals are separated from
non-metals by a staircase of elements called metalloids
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Properties of Metalloids
properties intermediate between metals and non-metals
silicon tellurium
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Chemical Families
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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
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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)
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Atom
An atom is the smallest part of an element that has all the element’s properties
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Atomic Theory
Each element has its own unique kind of atom Atoms of different elements vary in mass,
volume and reactivity
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Atomic Theory
Atoms are not the smallest particles of matter Subatomic particles combine together
to form atoms Protons Neutrons Electrons
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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
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Subatomic Particle Summary
Particle Charge Relative Mass Location Influences…
Proton
Neutron
Electron
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Subatomic Particle Summary
Particle Charge Relative Mass Location Influences…
Proton +
Neutron 0
Electron -
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Subatomic Particle Summary
Particle Charge Relative Mass Location Influences…
Proton + 1
Neutron 0 1
Electron - 1/2000
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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
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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
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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
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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
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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.
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Subatomic Particle Summary
Particle Charge Relative Mass Location Influences…
Proton + 1
Neutron 0 1
Electron - 1/2000
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Subatomic Particle Summary
Particle Charge Relative Mass Location Influences…
Proton + 1 Nucleus
Neutron 0 1 Nucleus
Electron - 1/2000 Shell
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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
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Subatomic Particle Summary
Particle Charge Relative Mass Location Influences…
Proton + 1 Nucleus
Neutron 0 1 Nucleus
Electron - 1/2000 Shell
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Subatomic Particle Summary
Particle Charge Relative Mass Location Influences…
Proton + 1 Nucleus Mass &Charge
Neutron 0 1 Nucleus Mass
Electron - 1/2000 Shell Charge
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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
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Bohr Model of the atom
the electrons in the valence shell are called valence electrons
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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
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Let’s look at an example…
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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
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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)
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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
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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.
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What’s wrong with this drawing?
The placement of electrons in the valence shell of this diagram is inaccurate
Premature pairing of electrons
S
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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
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Lewis dot diagrams
A drawing of an atom with ONLY it’s valence electrons
Example: Carbon
Example: Phosphorus
C
P
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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
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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
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Trends in the Periodic Table
What trends do you see in the number of valence electrons for each group?
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Trends in the Periodic Table
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
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Trends in the Periodic Table
What trends do you see in the number of orbitals for each period?
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Trends in the Periodic Table
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
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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.
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Counting Atoms Terms
Terms Example Atom count
Subscript Na3PO4
Brackets Mg3(PO4)2
Coefficient 2 H2O
3 Mg3(PO4)2
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Counting Atoms Terms
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