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Chemistry(14 - 16)
Chemistry(14 - 16)
The Atom(Basic Structure - 1)The Atom
(Basic Structure - 1)© SSER Ltd.
Atoms are minute particles of matter. A speck of dust contains billions of atoms.
As each individual atom is so tiny, it is impossible to see an individual atom in sufficient detail to describe its structure.
All matter throughout the Universe is made up of atoms.
The AtomThe Atom
The mass of an atom is very small and is not usually expressed in grams. One gram of hydrogen atoms will contain more than 600,000 million, million, million atoms!!!
The AtomThe Atom
Over the last two hundred years, scientific experiments have led us to a model of the atom which is widely accepted by modern scientists – this is known as the ‘Atomic Theory’.
Development of the Atomic TheoryDevelopment of the Atomic Theory
In 1806, the elements were defined by Dalton as being substances composed of onlyone type of atom.
We now define an element as a substance composed of atoms,each of which has the samenumber of protons.
John DaltonJohn
Dalton
He also introduced the ideathat atoms had a ‘solid ball’ structure.
John Dalton 1766 - 1844
In 1897, J. J. Thompson showed that an atom contained small negatively charged particles.
He called these particles electrons.
He proposed that the atom mustbe made of a positively charged sphere which contained the negatively charged electrons.
This became known as the ‘plum pudding’ model.
J. J. Thompson
J. J. Thompson
Thompson knew that the atom wasneutral (had no electrical charge).
J. J. Thompson 1856 - 1940 Positively charged
sphere
Negatively chargedelectron
In 1910, Earnest Rutherford and his research team carried out experiments in which particles were fired at a thin sheet of gold.
Earnest RutherfordEarnest Rutherford
Rutherford expected all of the particles to pass straight through...E. Rutherford 1871 - 1937
In 1910, Earnest Rutherford and his research team carried out experiments in which particles were fired at a thin sheet of gold.
Earnest RutherfordEarnest Rutherford
Rutherford expected all of the particles to pass straight through...E. Rutherford 1871 - 1937
Earnest RutherfordEarnest Rutherford
From these results, Rutherford concluded that the atom consisted of a central nucleus, which contained most of the atom’s mass, surrounded by the electrons. He also predicted the existence of neutrons in the nucleus.
Press ‘Start’ to take a closer look at Rutherford’s experiment...
The Structure of the AtomThe Structure of the AtomToday scientists accept that an atom contains a central nucleus around which electrons orbit in different levels.
The nucleus is composed of neutrons and protons.
Each element has a unique combination of the three types ofsub atomic particles...
N.B. This diagram represents a lithium atom. In reality, the electrons are very much smaller than the neutrons or protons.
The Structure of the AtomThe Structure of the Atom
= Protons = Electrons= Neutrons
Protons, neutrons, and electrons are types of sub-atomic particle.
An electron has an incredibly small mass, which is 1/1840 the mass of a neutron or a proton. Therefore, electrons are not considered to contribute anything to the mass of an atom. Hence, the vast majority of the mass of an atom is found in the nucleus.
The Atomic NucleusThe Atomic NucleusThe nucleus of an atom is tiny compared to the volume occupied by the electrons of the atom.
If an atom could be enlarged to the size of a football stadium, the nucleus of the atom would be about the size of a golf ball.
So far, the nucleus has been shown as a static body, whose sub-atomic particles fill the space of the nucleus. In fact, the nuclear particles are in constant motion.
The Atomic NucleusThe Atomic Nucleus
The charges on the proton and electron are opposite but equal in magnitude, so they cancel each other out exactly.
Protons
Electrons
Neutrons
Sub-Atomic Particles – Mass and ChargeSub-Atomic Particles – Mass and Charge
1
1
1/1840
Charge Mass
0
For each particle drag and drop the correct answers into the table.
The Atom – Sub Atomic ParticlesThe Atom – Sub Atomic Particles
Does the Atom have an Electrical Charge?Does the Atom have an Electrical Charge?
Total Charge = 0 + (+3) + (-3) = 0
All atoms have an overall neutral electrical charge and therefore any atom always has an equal number of protons and electrons.
= 3 Protons = 3 x +1 charge = +3
= 3 Electrons = 3 x -1charge = -3
= 4 Neutrons = 4 x 0 charge = 0
The atomic number is the number of protons in an atom.
To describe an atom fully, we need to know the numbers of each type of sub-atomic particle in the atom.
The Atom – Atomic Number and Atomic MassThe Atom – Atomic Number and Atomic Mass
The mass number is the sum of protons and neutrons in the atom.
N.B. The electrons have an insignificant mass.
We use these numbers to generate the atomic number and the mass number of the atom.
This shows that a Lithium (Li) atom hasthree protons, and four neutrons.
An atom of Lithium (Li) can be represented as follows:
7
3Li
Mass Number
Atomic Number
Atomic Symbol
The Atom – Atomic Number and Atomic MassThe Atom – Atomic Number and Atomic Mass
Li 7Mass Number
The Lithium AtomThe Lithium Atom
3Atomic Number
4 x 3 x 3 x
= Protons = Electrons= Neutrons
C 12Mass Number
6Atomic Number
The Carbon AtomThe Carbon Atom
6 x 6 x 6 x
= Protons = Electrons= Neutrons
All atoms of a particular element have the same number of protons and electrons. All lithium atoms have 3 protons and3 electrons whereas all carbon atoms have 6 protons and 6 electrons.
Therefore, the atoms of each different element have a unique number of protons and electrons.
The Lithium and Carbon AtomsThe Lithium and Carbon Atoms
The Carbon AtomThe Lithium Atom
Drag the following elements, based on their atomic number, into the correct place in the periodic table.
Atomic Structure and the Periodic TableAtomic Structure and the Periodic Table
The electrons fill the levels from the nearest level to the nucleus, outwards.
Each electron level has a maximum number of electrons it can hold.
In an atom, the electrons are arranged in levels (sometimes called shells or orbitals) around the nucleus.
Electron Levels (Shells)Electron Levels (Shells)
Electron Levels (Shells)Electron Levels (Shells)The first electron level can hold up to 2 electrons.
The second electron level can hold up to 8 electrons.
The third electron level can hold up to 18 electrons.
In this atom (Na) the first two electron levels are full but the third shell is incomplete.Note that only some nuclear particles are shown.
The Structure of AtomsThe Structure of AtomsElectrons do not orbit in concentric circles but have more elaborate orbits.
If the electrons in an atom were particles...and if we could freeze the atom at a moment in time!...and if we had a microscope that could see the atom!...is this what an atom would look like?
The Structure of AtomsThe Structure of Atoms
OR ... if the electrons in an atom were particles
…and in very rapid motion around the nucleus, so rapid that they appear as a blur...
...is this what an atom would look like?
The Structure of AtomsThe Structure of Atoms
2
2,8
2,8,18
The second level can hold 8 electrons
The third level can hold up to 18 electrons
Electron Levels (Shells)Electron Levels (Shells)The electrons in different levels (shells) are represented in the following way:
The first level can hold 2 electrons
2, 1
The Electronic Structure for LithiumThe Electronic Structure for LithiumLithium is the first element in the first short period of the Periodic Table. Its atomic number is 3, which tells us that an atom of lithium contains 3 electrons.
The electron configuration for a lithium atom can be drawn like this:
The electronic configuration for lithium is written as:
2, 8, 7
The Electronic Structure for ChlorineThe Electronic Structure for ChlorineChlorine is in the second short period of the Periodic Table. Its atomic number is 17, which tells us that an atom of chlorine contains 17 electrons.
The electrons in a chlorine atom fill the levels starting from the lower level.
The electronic configuration for chlorine is written as:
Electron Levels (Shells)Electron Levels (Shells)Drag the electrons to form the correct electronic configuration for neon (atomic number 10)…
Electron Levels (Shells)Electron Levels (Shells)
Type the correct electronic configurations of these four elements…
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