03 Atomic Structure
03 Atomic Structure alt
alt
03. Atom: Protons, Neutrons and Electrons 2
Atoms consist of a nucleus and a cloud of electrons that move around the nucleus. The nucleus is itself a cluster of two kinds of particles, protons and neutrons.
the electrons circle very fast around the nucleus, at different energy levels from it;
these energy levels are called shells
the protons and neutrons cluster together in the centre, forming the nucleus; this is the heavy part of the atom
Note how the electrons are orbiting around nucleus like planets around a solar system.
03. 1 The Atom
Atoms are the smallest particles of matter, that we cannot break down further by chemical means.
Atoms are mostly empty space. Each consists of a nucleus and a cloud of particles called electrons that whizz around it. This drawing shows how an atom might look like.
nucleus
electron cloud
03. Atom 3
Can you think of similarities and differences between how the solar system and the structure of an atom?
alt
03.5
•
What are subatomic particles?•
Name the particles that make up the atom.•
Which particle has:‣ A postive charge.
‣ No charge.
‣ Almost no Mass.
Skill Check
03. 6 Proton Number
The sodium atom is a good one to start with. It has 11 protons, 11 electrons, and 12 neutrons. They are arranged like this:
the electrons circle very fast around the nucleus, at different energy levels from it;
these energy levels are called shells
the protons and neutrons cluster together in the centre, forming the nucleus; this is the heavy part of the atom
A sodium atom has 11 protons. This can be used to identify it, since only a sodium atom has 11 protons. Every other atom has a different number.
You can identify an atom by the number of protons in it.
03. Atom: Protons, Neutrons and Electrons 4
Particle in atom Mass Charge
proton 1 unit positive charge (1!)
neutron 1 unit none
electron almost nothing negative charge (1")
Mass: Nucleus Proton Electron Charge: Nucleus Proton Electron
alt
03.8
•
An atom has 9 protons. Which element is it?•
Why do atoms have no overall charge?Skill Check
03.9
•
Name each of these atoms, and say how many protons, electrons, and neutrons it has:Skill Check
12C
6 168O 2412Mg 2713Al 6429Cu
03. 7 Nucleon Number
Protons and neutrons form the nucleus, so are called nucleons. The total number of protons and neutrons in an atom is called its nucleon number.
The nucleon number for the sodium atom is 23. (11 ︎P + 12 N =︎ 23) So sodium can be described in a short way like this:
The lower number is always the proton number. The other number is the nucleon number. So you can tell straight away that sodium atoms have 12 neutrons. (23 ︎- 11 =︎ 12)
So sodium can be described in a short way like this: 23 11 Na.
alt
03. A Table of Elements 11
18th century chemist, Dmitri Mendeleev, recognised the elements had properties repeating after every 8 or so elements. In other word the pattern of properties was Periodic.
Instead of listing down the elements in one column he made a table with 8 columns and called them groups. And he called the rows in his table Periods.
03. A Table of Elements 12
I II III IV V VI VII VIII
03. 10 A Table of Elements
Here are the first 12 elements, shown as a list:
Element Symbol Proton number Electrons Neutrons Nucleon number
(protons ! neutrons)
hydrogen H 1 1 0 1
helium He 2 2 2 4
lithium Li 3 3 4 7
beryllium Be 4 4 5 9
boron B 5 5 6 11
carbon C 6 6 6 12
nitrogen N 7 7 7 14
oxygen O 8 8 8 16
fluorine F 9 9 10 19
neon Ne 10 10 10 20
sodium Na 11 11 12 23
magnesium Mg 12 12 12 24
alt
03. 13 How to Identify an Atom
Only sodium atoms have 11 protons.
You can identify an atom by the number of protons in it.
03. 14 Isotopes
All carbon atoms have 6 protons. But not all carbon atoms are identical.
Some have more neutrons than others.
Most carbon atoms are like this, with 6 neutrons. That makes 12 nucleons (protons ! neutrons) in total, so it is called carbon-12.
But about one in every hundred carbon atoms is like this, with 7 neutrons. It has 13 nucleons in total, so is called carbon-13.
And a very tiny number of carbon atoms are like this, with 8 neutrons. It has 14 nucleons in total, so is called carbon-14.
6 protons 6 electrons 6 neutrons
126C 6 protons
6 electrons 7 neutrons
136C 6 protons
6 electrons 8 neutrons 146C
03. Isotopes 15
The three atoms in the previous slide are called isotopes of carbon.
Isotopes are atoms of the same element, with different numbers of neutrons.
Aside from their mass isotopes are identical in every other way.
alt
03. 16 Isotopes of Chlorine
Notice the atomic mass of chlorine is 35.5. The mass used there is relative atomic mass, which is just a fancy way of saying average mass.
Cl
35
17 3717
Cl
03. 17
•
What are isotopes?•
Name the three isotopes of carbon.•
Abundance of isotopes of chlorine-35 and chlorine 37 are 25% and and 75%. Calculate its average mass.Skill Check
03. 18 Electron Arrangement
Electrons are arranged in shells around the nucleus.
The first shell, closest to the nucleus, is the lowest energy level. The further a shell is from the nucleus, the higher the energy level.
The first shell can hold only 2 electrons. It fills first.
The second shell can hold 8 electrons. It fills next.
The third shell can hold 18 electrons. But it fills up to 8. The next 2 go into the fourth shell (not shown). Then the rest of the third shell fills.
nucleus
alt
03. 20 Valency
Valency is the number of electrons in the outer most shell of an atom.
You’ll see in coming chapters that valency plays a large role in chemical reactions.
03. Electron Arrangement 21
Note these patterns for the table of the first 20 elements:
•
The period number tells you how many shells there are.•
All the elements in a group have the same number of electrons in their outer shells. So Group I elements have 1, Group II have 2, and so on.These outer-shell electrons are also called the valency electrons.
•
The group number is the same as the number of outer-shell electrons, except for Group 0.03. Electron Arrangement 19
Below are the electron shells for the first 20 elements of the Periodic Table.
20 proton number
electron shells
electron distribution
II III IV V VI VII
Group I
Period 1
2
3
4
0 1
H 1 3
Li 2!1
4
Be 2!2
5
B 2!3
6
C 2!4
7
N 2!5
8
O 2!6
9
F 2!7
10
Ne 2!8 2
He2
2!8!8Ar 18
2!8!7Cl 17
2!8!6S 16
2!8!5P 15
2!8!4Si 14
2!8!3Al 13
2!8!2Mg 12
2!8!1Na 11
2!8!8!1K 19
2!8!8!2Ca
alt
2003.24
•
An element has 5 valency electrons. Which group is it in?•
4 How many electron shells do atoms of Period 3 have?•
The element krypton, Ar, is in Group 0, Period 3. Its proton number is 18.Skill Check 03.22
•
One element has atoms with 13 electrons.‣ Draw a diagram to show the electron distribution.
‣ Write the electron distribution in this form: 2+…
‣ Name the element.
Skill Check
03.23
•
The electron distribution for boron is 2︎ + 3. What is it for:‣ Lithium
‣ Magnesium
‣ hydrogen
Skill Check
alt
03.25
•
Draw the electrons for the first 20 elements. Use the periodic table for guidance.Skill Check
alt
alt
03 Atomic Structure - Formatives
Questions
Core curriculum
1 Particle Electrons Protons Neutrons
A 12 12 12
B 12 12 14
C 10 12 12
D 10 8 8
E 9 9 10
The table above describes some particles.
a Which three particles are neutral atoms?
b Which particle is a negative ion? What is the charge on this ion?
c Which particle is a positive ion? What is the charge on this ion?
d Which two particles are isotopes?
e Use the table on page 33 to identify A to E.
2 The following statements are about the particles that make up the atom. For each statement write:
p if it describes the proton e if it describes the electron n if it describes the neutron A the positively-charged particle B found with the proton, in the nucleus
C the particle that can occur in different numbers, in atoms of the same element
D held in shells around the nucleus E the negatively-charged particle F the particle with negligible mass
G the number of these particles is found by subtracting the proton number from the nucleon number
H the particle with no charge
I the particle with the same mass as a neutron J the particle that dictates the position of the
element in the Periodic Table 3 The atoms of an element can be
represented by a set of three letters, as shown on the right.
a What does this letter stand for?
i X ii y iii z
b How many neutrons are there in these atoms?
i 107 47 Ag ii 63 29 Cu iii 1 1 H iv 20 10 Ne v 238 92 U c Bromine atoms have 36 neutrons. Describe a
Revision checklist
Core curriculum Make sure you can …
define these terms:
atom element compound
say where in the atom the nucleus is, and which particles it contains
define proton number and nucleon number
state the number of protons, neutrons and electrons in an atom, from a short description like this: 23 11 Na explain what a radioisotope is
give one medical and one industrial use, for radioisotopes
sketch the structure of an atom, showing the nucleus and electron shells
state the order in which electrons fill the electron shells
name the first 20 elements of the Periodic Table, in order of proton number, and give their symbols sketch the electron distribution for any of the first
20 elements of the Periodic Table, when you are given the proton number
show electron distribution in this form:
2 ! 8 ! …
define the term valency electron
state the connection between the number of valency electrons and the group number in the Periodic Table
state the connection between the number of electron shells and the period number in the Periodic Table
work out the electron distribution for an element, given its period and group numbers
say how many outer-shell electrons there are in the atoms of Group 0 elements
explain why the Group 0 elements are unreactive point out where the metals and non-metals are, in
the Periodic Table
give at least five key differences between metals and non-metals
name and give the symbols for the common metals and non-metals (including metals from the
transition block of the Periodic Table)
y
X
alt
zand sulfur (S), write down:
a i which period of the Periodic Table it belongs to
ii its group number in the Periodic Table iii its proton number
iv the number of electrons in its atoms v its electronic configuration
vi the number of outer electrons in its atoms b The outer electrons are also called the _____
electrons. What is the missing word? (7 letters!) c Which of the above elements would you expect
to have similar properties? Why?
5 Boron has two types of atom, shown below.
a What is different about these two atoms?
b What name is given to atoms like these?
c Describe each atom in shorthand form, as in 3.
d What is the nucleon number of atom A?
e Is atom B heavier, or lighter, than atom A?
f i Give the electronic configuration for A and B.
ii Comment on your answer for i.
6 The two metals sodium (proton number 11) and magnesium (proton number 12) are found next to each other in the Periodic Table.
a Say whether this is the same, or different, for their atoms:
i the number of electron shells
ii the number of outer (valency) electrons The relative atomic mass of sodium is 23.0.
The relative atomic mass of magnesium is 24.3.
b Which of the two elements may exist naturally as a single isotope? Explain your answer.
7 Strontium, proton number 38, is in the fifth period of the Periodic Table. It belongs to Group II.
Copy and complete the following.
An atom of strontium has:
an atom of an element.
a i Give the electron distribution for the atom.
ii What is special about this arrangement?
b Which group of the Periodic Table does the element belong to?
c Name another element with the same number of outer-shell electrons in its atoms.
9 Gallium exists naturally as a mixture of two non- radioactive isotopes, gallium-69 and gallium-71.
The proton number of gallium is 31.
a i How many neutrons are there in gallium-69?
ii How many neutrons are there in gallium-71?
Gallium also has a radioactive isotope, gallium-67.
As gallium-67 decays, it gives out rays called gamma rays.
b How does the radioactive isotope differ from the non-radioactive isotope?
c Name two possible uses, one medical and one non-medical, for gallium-67.
10 Read this passage about metals.
Elements are divided into metals and non-metals.
All metals are electrical conductors. Many of them have a high density and they are usually ductile and malleable. All these properties influence the way the metals are used. Some metals are sonorous and this leads to special uses for them.
a Explain the underlined terms.
b Copper is ductile. How is this property useful in everyday life?
c Aluminium is hammered and bent to make large structures for use in ships and planes. What property allows it to be shaped like this?
d Name one metal that has a low density.
e Some metals are cast into bells. What property must the chosen metals have?
f Give the missing word: Metals are good conductors of ... and electricity.
g Choose another physical property of metals, and give two examples of how it is useful.
h Phosphorus is a solid non-metal at room temperature.What other physical properties
atom A atom B
proton neutron electron
alt
and sulfur (S), write down:
a i which period of the Periodic Table it belongs to
ii its group number in the Periodic Table iii its proton number
iv the number of electrons in its atoms v its electronic configuration
vi the number of outer electrons in its atoms b The outer electrons are also called the _____
electrons. What is the missing word? (7 letters!) c Which of the above elements would you expect
to have similar properties? Why?
5 Boron has two types of atom, shown below.
a What is different about these two atoms?
b What name is given to atoms like these?
c Describe each atom in shorthand form, as in 3.
d What is the nucleon number of atom A?
e Is atom B heavier, or lighter, than atom A?
f i Give the electronic configuration for A and B.
ii Comment on your answer for i.
6 The two metals sodium (proton number 11) and magnesium (proton number 12) are found next to each other in the Periodic Table.
a Say whether this is the same, or different, for their atoms:
i the number of electron shells
ii the number of outer (valency) electrons The relative atomic mass of sodium is 23.0.
The relative atomic mass of magnesium is 24.3.
b Which of the two elements may exist naturally as a single isotope? Explain your answer.
7 Strontium, proton number 38, is in the fifth period of the Periodic Table. It belongs to Group II.
Copy and complete the following.
An atom of strontium has:
an atom of an element.
a i Give the electron distribution for the atom.
ii What is special about this arrangement?
b Which group of the Periodic Table does the element belong to?
c Name another element with the same number of outer-shell electrons in its atoms.
9 Gallium exists naturally as a mixture of two non- radioactive isotopes, gallium-69 and gallium-71.
The proton number of gallium is 31.
a i How many neutrons are there in gallium-69?
ii How many neutrons are there in gallium-71?
Gallium also has a radioactive isotope, gallium-67.
As gallium-67 decays, it gives out rays called gamma rays.
b How does the radioactive isotope differ from the non-radioactive isotope?
c Name two possible uses, one medical and one non-medical, for gallium-67.
10 Read this passage about metals.
Elements are divided into metals and non-metals.
All metals are electrical conductors. Many of them have a high density and they are usually ductile and malleable. All these properties influence the way the metals are used. Some metals are sonorous and this leads to special uses for them.
a Explain the underlined terms.
b Copper is ductile. How is this property useful in everyday life?
c Aluminium is hammered and bent to make large structures for use in ships and planes. What property allows it to be shaped like this?
d Name one metal that has a low density.
e Some metals are cast into bells. What property must the chosen metals have?
f Give the missing word: Metals are good conductors of ... and electricity.
g Choose another physical property of metals, and give two examples of how it is useful.
h Phosphorus is a solid non-metal at room
atom A atom B
proton neutron electron
