a. atoms and atomic structure
TRANSCRIPT
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Lower Secondary Science 1Atoms and Atomic Structure
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To enable students to: Understand what an atom is Understand that atom is made up ofsubatomic particles in of distinct
characteristics Understand the arrangement of electrons in the atom of first twenty
element Represent arrangement of electrons for first twenty elements in full and
simplified electronic configuration Understand what a periodic table is Understand what a period of a periodic table is and, the trend of
elements in a period and the characteristics of elements in the same
period Understand what a group of periodic table is and the characteristics of
elements in the same group Understand how to calculate the number of protons, electrons and
neutrons given the mass number and atomic number of an element. Know how to derive the number of protons, electrons and neutrons
given any of the other values or from periodic tableLower Secondary Science Atoms and Atomic Structure 2
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Element is made up of tiny particles, called atom.
Each element consists of the same type of atoms.
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Atoms is the smallest particle of an element.
Lower Secondary Science 5Atoms and Atomic Structure
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How small is an atom?
Object Length in metres
Length of a housefly 0.05
Size of a dust particle 0.0001
Diameter of a strand of hair 0.00006
Size of a bacteria 0.000001
Diameter of a hydrogen atom 0.0000000001
Lower Secondary Science 6Atoms and Atomic Structure
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atomos, an ancient Greek word meaning indivisible.
The Greek philosopher Demokritos (460-370 BCE)maintained that all matter could be divided and sub-
divided into smaller and smaller units, and
eventually there would be a tiny particle that could
not be divided any further - an atom.
Proven by scientific experiment by John Dalton in
the 1800s
Lower Secondary Science 7Atoms and Atomic Structure
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Lower Secondary Science Atoms and Atomic Structure 8
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An atom consists mostly of empty space.
An atom has a nucleus in the centre and made up
of 3 sub-atomic particles, protons, neutrons andelectrons.
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Lower Secondary Science Atoms and Atomic Structure 10
The nucleus containspositively charged
protons and neutrons,
which are tightly packed.
An at c n i t
tly fempty
space.
Negatively chargedelectrons ve
ar und the nucleu
in fixed orbits r
path .
An at ha a nucleus,
den ely c ncentrated in
the centre.
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Proton
Found in the nucleus which is inthe centre of an atom.
Carries a charge of +1.
Has relative mass of 1.
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Electrons
Found in electron shells whichsurround the atom.
Carries a charge of -1.
Has negligible mass or relativemass of 1/2000.
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Lower Secondary Science Atoms and Atomic Structure 14
SubatomicP
articl
es
Relative
Charge
Relative
mass
Location
Neutron 0 1 Nucleus
Proton +1 1 Nucleus
Electron -1 1/2000 Electron shells
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Lower Secondary Science Atoms and Atomic Structure 15
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Lower Secondary Science Atoms and Atomic Structure 16
An atom is electrically neutral
** number of protons= number of electrons
Subat icParticles
elativear e
Totalar e
Electron -1 -6
roton 1 6
Neutron 0 0
Mass number = 12Proton number = 6
It has:6 protons6 electrons6 neutrons
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A neutron walked into a bar and asked, How
much for a drink?
What did the bartender reply?
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Is Ferrero Roche a good representation of an atom?
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Electronic structure/configuration:The way
the electrons are arranged in an atom
Determined by energy levels around the
nucleus of an atom.
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Each energy level can accommodate adefinite number of electrons.
First 20 elements (Hydrogen to Calcium) 1st energy level (nearest to nucleus) : 2 electrons
2nd energy level : 8 electrons
3rd energy level : 8 electrons 4th energy level: 8 electrons
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Lower Secondary Science Atoms and Atomic Structure 21
Shell numberfrom nucleus
Maximumnumber of
electrons1 2
2 4
3 44 4
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Lower Secondary Science Atoms and Atomic Structure 22
Consider aHydrogen atom (1 electron):
Consider aHelium atom (2 electrons):
HH
Hydrogen atom only has 1
electron, so the first shell gets
to fill up first.
HeHe
Helium atom has 2 electrons
and fill up the first shell.
H
He
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Consider Lithium atom:
The above is called a full electronic structure of alithium atom
Simplified electronic structure (Electron Configuration)of a lithium atom: 2.1
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LiLi
Lithium has 3 electrons.First 2 electrons fill up the
first shell.
The 3rd electron fills up the2nd shell.
Li
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The above is called a fullelectronic structure of acalcium atom
Simplified electronic
structure (E
lectronConfiguration)of alithium atom: 2.8.8.2
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Ca
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Draw the full electronic structure for these atoms:
Boron (5 electrons)
Oxygen (8 electrons) Magnesium (12 electrons) Chlorine (17 electrons)
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Lower Secondary Science Atoms and Atomic Structure 26
Element Protonnumber Electronic onfi uration
H 1 1
He 2 2
Li 3 2.1e 2.2
5
6 2.
N 7
O 2.6
F 9
Ne 1 2.
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Lower Secondary Science Atoms and Atomic Structure 27
Element Proton number Electronic Configuration
Na 11 2.8.1
Mg 12 2.8.2
Al 13Si 14
P 15
S 16 2.8.6
Cl 17
Ar 18
K 19
Ca 20 2.8.8.2
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Electrons in the outermost shell valence
electrons.
Valence electrons of the atom are the electrons
that take part in chemical reactions.
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Lower Secondary Science Atoms and Atomic Structure 29
gas at room temperature
liquid at room temperature
solid at room temperature
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A horizontal period in the PeriodicTable contains
elements with the same number of electron
shells.
A vertical group in the PeriodicTable containselements with the same number of electrons in
the outermost (valence) shell.
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A symbol gives information faster than words.
No smoking
Radioactive
Road Work
Toilet
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Different languages across the world
Need to set a standard name that will be recognised byeveryone.
Hence, each element given an internationallyrecognised chemical symbols.
Syre
ZuurstofSauerstoff
Oxygne
Oxygen
Swedish
DutchGerman
French
English
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Each element represented by a chemical symbol of oneor two letters, usually from its name.
The first letter in a chemical symbol is always capitalised
and any other letter that follows is in the lower case. When the chemical symbol is only one letter, it is usually
the first letter of its English name
Example
There are two exceptions
Hydr ge HBoron B
Carbon C
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For two-letter symbols, it may or may not be made up ofthe first two letters of its English name
Example
For some two-letter symbols, the letters do not come
from its English name at all Example
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Lithium Li
Calcium Ca
Magnesium Mg
Chlorine Cl
Copper Cu
Iron Fe
Lead Pb
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The mass number/nucleon number of an element is thesum of the number of protons and the number ofneutrons contained in one atom of the element.(mass number = number of protons + number of neutrons)
The atomic number/proton number of an element isthe number of protons contained in one atom of anelement.
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SymbolMass No.
Atomic No.Xba
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Na23
11
Atomic number =_______
Mass number =________
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Lower Secondary Science Atoms and Atomic Structure 37
Na
23
11
number of protons = 11number of electrons = 11(hint: number of protons equals number of electrons)
number of neutrons = 23-11= 12
(hint: mass number =number of protons + number of neutrons)
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Lower Secondary Science Atoms and Atomic Structure 38
Ca
40
20
Mass number =_______
Atomic number =_______
No. of protons =No. of electrons =No. of neutrons =
Cr
52
24
Mass number = ________
Atomic number = ________
number of protons =number of neutrons =number of electrons =
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Fill in the table with the correct value
Proton Electron Neutron Atomic
Number
Mass
NumberPhosphorus 15 16
Zinc 30 30 65
Arsenic 42 33
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I am able to:
Define what is atom
Explain the structure of atom with its sub-particles
Explain the characteristics of sub-particles Define mass/nucleon number and atomic/proton number
State the mass/nucleon number and atomic/proton number of agiven element
State the number of protons, electrons and neutron of a givenelement
Explain the electronic configuration of an atom
Draw the electronic structure and write the configuration of agiven element
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