Transcript Atomic Structure - Cambridge College Secondary Science

L
C3 Atomic Structure & the
Periodic table
Get your periodic tables out!
Elements song!
http://www.privatehand.com/flash/elements.html
Groups &
periods (rows)
The Periodic Table
If a substance is made up of only one type of atom
we say it is an element. For example, consider a
tripod made up of iron
These atoms are
ALL iron – there’s
nothing else in here
C3/3.3 Learning Objectives
• Describe the structure of an atom in terms of electrons
and a nucleus containing protons & neutrons.
• State the relative charges & approximate relative
masses of protons, neutrons and electrons.
• Define proton number & nucleon number.
• Use proton number and the structure of an atom to
explain the basis of the periodic table with reference to
first 20 elements
• Define Isotopes.
Learning Objectives
• Describe the build-up of electrons in
‘shells’ and understand the significance of
the noble gas electronic structures and of
valency electrons.
1) Atoms!
Atoms are the basic building blocks of matter that make up
everyday objects.
People thought that atoms were the smallest particles and could
not be broken into anything smaller.
proton
neutron
electron
What can you say about the size of the electron
compared to the neutron & proton
What do you know…
• Form a giant atom.
• Atoms consist of protons, neutrons &
electrons-form a giant atom as a class
or as groups
What is the structure of an atom?
Protons, neutrons and electrons are not evenly distributed in an atom.
Pea in a
football pitch
The protons and neutrons exist in a
dense core at the centre of the atom.
This is called the nucleus.
The electrons are spread out
around the edge of the atom.
They orbit the nucleus in
layers called shells.
Mass and electrical charge
There are two properties of protons, neutrons and electrons that are
especially important:
 mass
 electrical charge.
Particle
Mass
Charge
proton
1
neutron
1
electron
almost 0
+1
0
-1
2) Atomic Number & Mass Number (Nucleon number)
Mass Number - The larger number.
Mass number= number of protons + number of
neutrons
Atomic Number/ Proton NumberNumber of protons equals number of
electrons.
What is sodium’s atomic number?
How many protons does it have?
How many electrons does it have?
What is its Mass Number?
How many neutrons does it have?
number of neutrons = mass number - number of protons
= mass number - atomic number
=23 – 11
=12 Neutrons
Periodic table
• Elements in the periodic table are arranged in
order of atomic number!
Mini-Whiteboards
Hydrogen
1 proton
0 neutrons
1 electron
Fluorine
9 Protons
10 Neutrons
9 Electrons
Magnesium
12 Protons
12 Neutrons
12 Electrons
Carbon
6 Protons
6 Neutrons
6 Electrons
Oxygen
8 Protons
8 Neutrons
8 Electrons
Iron
26 Protons
30 Neutrons
26 Electrons
Tin
50 Protons
69 Neutrons
50 Protons
Equal numbers of protons and electrons
Atoms of elements have no charge, they are neutral.
What is the charge on a fluorine atom?
19
9 protons
9 electrons
10 neutrons
charge = +9
charge = - 9
charge = 0
F
9
Total charge =
0
How are the number of electrons and atomic number related in a
neutral atom?
They are the same.
Isotopes
• Different forms of the same atoms can exist.
• These are called Isotopes
• Isotopes are different forms of the same element
that have the same atomic number but different mass
numbers.
Isotopes
An isotope is an atom with a different number of neutrons:
Notice that the mass number is different. How many
neutrons does each isotope have?
Each isotope has 8 protons – if it didn’t then it just
wouldn’t be oxygen any more.
Progress check
1)
Name the sub-atomic particles within an atom. (3)
2)
Explain why atoms are overall neutral in charge. (2)
3)
Complete the missing numbers (11)
Self assessed answers
1)Protons, neutrons & electrons.
2)Atoms are neutral as protons (positive charge)
are equal to the number of electrons (negative
charges)
3)
Boron-5,11
Potassium 19,20
Chromium 24,52
Mercury 80,80
Argon 18,22,18
Question 4: Identifying Isotopes
4a) What is an isotope?
4b)Identify the isotopes from data about the
number of electrons, protons and neutrons:
1)
2)
3)
4)
1 proton, 1 electron, 2 neutrons
1 proton, 1 electron, 1 neutron
17 protons, 17 electrons, 19 neutrons
85 protons, 85 electrons, 126 neutrons
3
1
H
2
1
H
36
17
Cl
211
85
At
3) Electrons
• The protons & Neutrons are found in
the............
• Electrons have a special home of their own.
Electrons are found on ENERGY
LEVELS also known as Shells!
These energy levels can only house a
certain number of electrons.
Electron Shells
Electrons will fill the shells nearest the nucleus
first.
1st shell holds
a maximum of
2 electrons
2nd shell holds
a maximum of
8 electrons
3rd shell holds
a maximum of
8 electrons
This electron arrangement is written as 2,8,8.
What if you have more than 18 electrons..where does the extra
electron go?...
Tasks
• Mats & Play Dough
• Take a tub between 3 and use this to
represent your electrons.
• Complete the electron arrangement for
the following:
F, Mg, Si,
Extension: (Ar, Ca)
Electron arrangement
• Electron configuration for first 20
elements.
• Draw and write it down, eg, 2,8,1
Question
Table 1
1-2
Table 2
Table 3
Table 4
Anika &
Sayeeda &
Moushomi Shamina
Syeda H &
Rahima
Adama &
Shaheena
3-4
Leigh &
Shahnaz
Samiha &
Nadia
Sadia &
Sima
Momtaz &
Abisola
5-6
Fahmida
&Cara
Ruma &
Shema
Nasima
Forida
Extension questions
Answers
•
•
•
•
•
•
•
•
Q1-All have 1 outer electron.
Q2-Both have 7 electrons in their outer shell
Q3-The group number tells us the number of outer electrons.
Q4-Group 8 Noble gases-unreactive
Q5-Iodine-7
Arsenic-5
Barium-2
Q6-First electron furthest away easiest to remove. Greater distance
between electrons and nucleus.
• Next eight increasingly harder to remove.
• Next 2 closest to shell-hardest-greater nucleus attraction-shorter distance
from nucleus to electrons.
Giant atom
• Form a giant atom using what you have
learnt today.
Exam quest
Questions- linked to learning objectives
Learning objectives-linked to exam quest
• (D) Describe the structure of the atom in terms of protons,
neutrons and electrons. Question 1
• (C) Identify symbols and atomic numbers using a Periodic Table.
(C) State that elements are arranged in ascending atomic
number. Question 2& 3
• (B) Identify the group of an element from its outer electrons
and row from it shells. Question 4
• (B) Deduce the number of protons, neutrons and electrons in a
particle and identify isotopes. Question 5
• (B) Deduce the electronic structure of the first 20 elements.
Question 6
• (A) Explain why an atom has a neutral charge. Question 7 if you
can answer WHY? To part 7bii-even better!
Giant atom
• Form a giant atom using what you have
learnt today.
Extras
Building a nucleus
Summary: the atom so far
The nucleus is:
 Made up of protons and neutrons
 Positively charged because of the
protons
 Dense – it contains nearly all the mass
of the atom in a tiny space.
Electrons are:
 Very small and light, and negatively charged
 Able to be lost or gained in chemical reactions
 Found thinly spread around the outside of the nucleus,
orbiting in layers called shells.