structure of atoms next > in this presentation you will: explore the structure of atoms
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Structure of Atoms
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In this presentation you will:
explore the structure of atoms
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Atoms are the smallest part of an element that can exist.
It used to be thought that atoms could not be subdivided.
However, we now know that atoms are made up of protons, neutrons and electrons.
Introduction
Atoms are the building blocks for the whole Universe.
Matter is composed of elements, which are made from small particles called atoms.
Physical substances are composed of matter.
Atoms are the smallest distinguishable part of an element. Each element, such as gold, is composed of just one type of atom. Next >
Atoms
Atoms are not solid spheres of matter as was once thought.
Although atoms are the smallest distinguishable unit of an element, they are made up of three different sub-atomic particles:
Protons
ElectronNeutronProton
Example: carbon atom (C)
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Neutrons
Electrons
Atoms
Unfortunately an atom is too small to be seen with the naked eye.
It is also too small to be seen with a normal light microscope.
We can draw a model to represent the atom.
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Models
ElectronNeutronProton
Example: carbon atom (C)
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This model will have advantages and disadvantages.
A good model will have more advantages than disadvantages.
This does not mean that the model is perfect.
Models
It is a way for us to understand better how the atom is constructed.
ElectronNeutronProton
Example: carbon atom (C)
What is the name given to the smallest distinguishable unit of an element?
A) Atom
B) Molecule
C) Particle
D) Matter
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Question 1
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What is the name given to the smallest distinguishable unit of an element?
Question 1
A) Atom
B) Molecule
C) Particle
D) Matter
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Example: carbon atom (C)Protons and neutrons are found in the middle of the atom, the nucleus.
Electrons are much smaller than the nucleons, and orbit (move around) the nucleus at a considerable distance from it.
Electron
Nucleus (consisting of protons
and neutrons)
Atoms
For this reason, protons and neutrons are often called nucleons.
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For example, if an atom was a soccer field, then the nucleus would be about the size of a soccer ball in the center of the field.
The rest of the atom is empty space.
Atoms
Example: carbon atom (C)
Electron
Nucleus (consisting of protons
and neutrons)
Which of the following is NOT found in the nucleus of any atom?
A) Proton
B) Neutron
C) Nucleon
D) Electron
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Question 2
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Which of the following is NOT found in the nucleus of any atom?
Question 2
A) Proton
B) Neutron
C) Nucleon
D) Electron
Protons, neutrons and electrons have different masses and electrical charges.
Both the masses and the charges are very, very small.
But then these particles are also very, very small.
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Particle NameMass in
kilogramsCharge in coulombs
Proton 1.7 × 10-27 +1.6 × 10-19
Neutron 1.7 × 10-27 0
Electron 9.1 × 10-31 -1.6 × 10-19
Mass and Charge
If you could fill a 1 cm cube just with protons or neutrons it would have a mass of 250 million tons!
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Particle Name Relative MassRelative Charge
Proton 1 +1
Neutron 1 0
Electron -1
Relative Mass and Charge
Nearly all the mass of an atom is in the positively charged nucleus.
We take the mass of the proton as 1 and its charge as +1 then compare the masses and charges of the other particles to the proton's values.
1
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Another way of comparing these quantities is to use their relative values.
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Relative Mass and Charge
The electron mass is nearly nothing compared with that of the proton and neutron.
It is electrical attraction between the positively charged nucleus and the negatively charged electrons that keeps the electrons orbiting the nucleus.
Particle Name Relative MassRelative Charge
Proton 1 +1
Neutron 1 0
Electron -11
1836
The identity of an atom is determined by the number of protons it contains.
For example, the simplest atom, hydrogen (H) always has one proton.
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Atomic Number
All atoms of the same element have the same number of protons.
Example: hydrogen atom (H)
One proton in the nucleus
One electron
Example: carbon atom (C)
6 Electrons
6 protons in the nucleus
The atomic number is equal to the number of protons in an atom's nucleus.
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An atom of carbon (C) always has six protons.
An element is determined by the atomic number of its atoms. Every element has a different atomic number.
Atomic Number
Example: carbon atom (C)
Atomic number = 6
Example: hydrogen atom (H)
Atomic number = 1
Example 2: Oxygen (O)The number of neutrons within an atom can be found by subtracting the atomic number from the mass number.
The mass number of an atom is the total number of protons and neutrons in the nucleus.
Example 1: Magnesium (Mg)
12 protons and12 neutrons
8 protons and8 neutrons
Mass number = 24
Mass number = 16
Atomic number = 12
Atomic number = 8
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Mass Number
Atoms of the same element with different numbers of neutrons, and therefore different atomic masses, are called isotopes.
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Atoms of an element always have the same number of protons.
Isotopes
Some atoms of the element may have different numbers of neutrons.
Hydrogen - 1 Hydrogen - 2
Two types of hydrogen
Electron
Proton Neutron
Many of the most common and important elements have several naturally occurring isotopes.
Carbon (C), which is found in all living things, has three isotopes: carbon-12, carbon-13 and carbon-14.
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Isotopes
Carbon-12Mass number = 12Atomic number = 6
Carbon-13Mass number = 13Atomic number = 6
Carbon-14Mass number = 14Atomic number = 6
Carbon-12Mass number = 12Atomic number = 6
Carbon-13Mass number = 13Atomic number = 6
Carbon-14Mass number = 14Atomic number = 6
Isotopes that naturally break down in this way (unstable) are called radioactive isotopes.
Carbon-12 is by far the most common isotope of carbon.
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Carbon-13 is found in smaller quantities, and carbon-14 is very rare as it easily breaks down into smaller particles.
Stable
Stable
Unstable (radioactive)
Isotopes
Information of any element can be found on a special chart known as ‘The Periodic Table’.
Each cell in the table shows an element and enables us to look up and compare the elements.
2
HeHelium
4
Atomic Number
Symbol
Name
Mass Number
Typical Cell from The Periodic Table
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The Periodic Table
The Periodic Table shows all the known elements in the universe. It also shows information such as the atomic number and mass number.
Elements are arranged into rows (periods) and columns (groups). Next >
The Periodic Table
1
2
3
4
5
6
7
1
2
3 4 5 6 7 8 9 10 11 12
13 14 15 16 17
18
Pe
riod
s
Groups
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Electron Structure
All chemical reactions are based around changes to the number and location of the electrons orbiting the nucleus.
All atoms of elements have the same number of protons (charge +1) as electrons (charge -1), so their net charge is zero.
The number and arrangement of electrons within an atom, determines the properties of an atom.
Example: neon atom (Ne)
ElectronProton Neutron
''Isotopes are atoms of the same element containing the same number of protons and electrons but different numbers of neutrons.''
Is this statement true or false?
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Question 3
True
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''Isotopes are atoms of the same element containing the same number of protons and electrons but different numbers of neutrons.''
Is this statement true or false?
Question 3
Each electron in an atom is in a particular energy level (or shell) and the electrons must occupy the lowest available energy level.
Electrons move rapidly around the nucleus (orbit) in distinct energy levels (shells).
When a shell is full the next electron goes into the next lowest available energy level.
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Example: nickel atom (Ni)
Increasing energy of energy levels
Energylevels (shells)
Electron Structure
2nd shell = 8 electrons
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1st shell = 2 electrons
Each energy level is capable of holding only a certain number of electrons.
The first energy level can hold only two electrons.
The second energy level can hold eight electrons.
Electron Structure
This energy level is filled first.
This energy level is filled after the first energy level is complete (full).
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There are further energy levels, each containing larger numbers of electrons.
The electrons in the outer shell are termed valence electrons.
Electron Structure
Outer shells
Electrons move rapidly around the nucleus in distinct orbits (energy levels). The second energy level can hold a maximum of…
A) one electron.
B) ten electrons.
C) eight electrons.
D) eighteen electrons.
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Question 4
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Electrons move rapidly around the nucleus in distinct orbits (energy levels). The second energy level can hold a maximum of…
A) one electron.
B) ten electrons.
C) eight electrons.
D) eighteen electrons.
Question 4
The reactivity of elements is the ability of a substance to react with another chemical substance to produce new products.
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The reactivity of an element is determined entirely by its valence electron configuration.
Reactivity and Valence Electrons
This is because these electrons are on the outside furthest from the nucleus and nearest to other atoms.
More reactive elements have atoms containing nearly empty or nearly full outer energy levels.
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Fluorine (F) is a very reactive element due to 7 electrons in the 2nd outer energy level (shell).
Neon (Ne) is a stable element, as it has a full outer energy level (shell).
Reactivity and Valence Electrons
These electron arrangements are said to be stable.
Elements with atoms that have a full outer energy level are very unreactive.
This model works well. It must do, as you will find it in many textbooks and reference sources.
Advantages:
It allows us to visualize something that is too small to see.
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It is not perfect.
It gives us an analogy with the solar system model.
It represents the energy levels (shells) as orbits.
How Good is this Model?
Disadvantages:
It simplifies and so distorts reality.
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It particularly misrepresents electron behavior (but represents energy levels well).
The scale is not correct.
How Good is this Model?
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The Electron Cloud
It is not possible to say where an electron is at any instant.
This is an improved model.
Electrons do not orbit the nucleus in circular orbits like satellites.
They rotate about the nucleus in "electron clouds".
We talk about the probability of where an electron is. The electron cloud represents the areas of highest probability.
NucleusElectron Clouds
In this presentation you have seen:
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how protons, neutrons and electrons are arranged in atoms
how models can be used to represent concepts
Summary