a. atoms and atomic structure

8/8/2019 A. Atoms and Atomic Structure

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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.

Lower Secondary Science Atoms and Atomic Structure 4


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Atoms is the smallest particle of an element.



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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



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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



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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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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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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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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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Shell numberfrom nucleus

Maximumnumber of

electrons1 2

2 4

3 44 4


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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


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


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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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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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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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


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.


SymbolMass No.

Atomic No.Xba


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Na23

11

Atomic number =_______

Mass number =________


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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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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


a. atoms and atomic structure

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