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What is an atom?What is an atom?
• All matter is made up of atoms.
• An atom is defined as the smallest particle of an element that can exist.
• All matter is made up of atoms.
• An atom is defined as the smallest particle of an element that can exist.
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How big is an atom?How big is an atom?
..
Contains about 1016 atoms!!!Contains about 1016 atoms!!!
2 million times more than humans in the world.
2 million times more than humans in the world.
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Why do we change models?Why do we change models?
• Old models are discarded or revised when they are found to be unsatisfactory in explaining certain phenomena.
• Models are continuously being revised as new evidence is gathered.
• Old models are discarded or revised when they are found to be unsatisfactory in explaining certain phenomena.
• Models are continuously being revised as new evidence is gathered.
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How big is an atom?How big is an atom?
• A scanning tunnelling microscope (STM) is used to observe atoms.
• Atoms have an average diameter of about 0.1nm.
• A scanning tunnelling microscope (STM) is used to observe atoms.
• Atoms have an average diameter of about 0.1nm.
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Use your imagination!Use your imagination!
1803, John Dalton1803, John Dalton In 1897, JJ ThomsonIn 1897, JJ Thomson
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Use your imagination!Use your imagination!
1911, Ernest Rutherford1911, Ernest Rutherford 1915, Niel Bohr1915, Niel Bohr
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Present your drawingPresent your drawing
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Development of the atomic modelDevelopment of the atomic model
2500 years ago,
Democritus:
“Matter is made up of
tiny individual
particles called atoms.”
2500 years ago,
Democritus:
“Matter is made up of
tiny individual
particles called atoms.”
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Development of the atomic modelDevelopment of the atomic modelIn 1803, John Dalton:
“ - All matter is made up of small indivisible particles called atoms” - Atoms of the same elements are alike - Different elements have different types of atoms - Atoms cannot be created, destroyed or changed - Compounds are formed when two or more elements combine”
In 1803, John Dalton:
“ - All matter is made up of small indivisible particles called atoms” - Atoms of the same elements are alike - Different elements have different types of atoms - Atoms cannot be created, destroyed or changed - Compounds are formed when two or more elements combine”
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Development of the atomic modelDevelopment of the atomic modelIn 1897, JJ Thomson:
“ - An atom is a continuous mass of positive charges containing negative charges called electrons. - The electrons are like the plums in a pudding of positive charges or raisins in a cake.”
In 1897, JJ Thomson:
“ - An atom is a continuous mass of positive charges containing negative charges called electrons. - The electrons are like the plums in a pudding of positive charges or raisins in a cake.”
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Development of the atomic modelDevelopment of the atomic modelIn 1911, Ernest Rutherford:
“ - An atom has a small, dense and positively charged nucleus in the centre, surrounded by negatively charged electrons circling around it, just like planets orbiting around the Sun. - Most of the atom is empty space.”
In 1911, Ernest Rutherford:
“ - An atom has a small, dense and positively charged nucleus in the centre, surrounded by negatively charged electrons circling around it, just like planets orbiting around the Sun. - Most of the atom is empty space.”
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Development of the atomic modelDevelopment of the atomic model
In 1915, Niel Bohr:“ - An atom has a small, dense nucleus made up of positively charged protons and electrically neutral neutrons. - The negatively charged electrons move around the nucleus in fixed orbits. - Only a certain number of electrons can be found in each orbit.”
In 1915, Niel Bohr:“ - An atom has a small, dense nucleus made up of positively charged protons and electrically neutral neutrons. - The negatively charged electrons move around the nucleus in fixed orbits. - Only a certain number of electrons can be found in each orbit.”
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Development of the atomic modelDevelopment of the atomic model
In 1926, Quantum Model of Atom:“ - Electrons do not move in fixed orbits. - They move around the nucleus in random paths. - Scientists can only predict the chance of finding the electrons in a particular region. - The regions where an electron is most likely to be found is called an orbital or electron density cloud.”
In 1926, Quantum Model of Atom:“ - Electrons do not move in fixed orbits. - They move around the nucleus in random paths. - Scientists can only predict the chance of finding the electrons in a particular region. - The regions where an electron is most likely to be found is called an orbital or electron density cloud.”
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Dalton’s modelDalton’s model
• Small solid spherical ball
• Small solid spherical ball
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Thomson’s modelThomson’s model
• Electrons distributed among a continuous mass of positive charges
• Electrons distributed among a continuous mass of positive charges
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Ernest Rutherford’s modelErnest Rutherford’s model
• Electrons orbiting around a small, dense positively charged nucleus
• Electrons orbiting around a small, dense positively charged nucleus
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Niel BohrNiel Bohr
• Electrons move round the nucleus in fixed orbits
• Electrons move round the nucleus in fixed orbits
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Quantum ModelQuantum Model
• Electrons move randomly and not in fixed orbits
• They are most likely to be found in the orbitals
• Electrons move randomly and not in fixed orbits
• They are most likely to be found in the orbitals
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What makes up an atom?What makes up an atom?
• An atom is the smallest particle of an element that can exist.
• The atom is made up of smaller particles called sub-atomic particles.
• An atom is the smallest particle of an element that can exist.
• The atom is made up of smaller particles called sub-atomic particles.
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Subatomic particlesSubatomic particles
Proton (+1) mass =1
Electron ( -1) mass = 1/1840
Neutron ( 0 ) mass= 1
Proton (+1) mass =1
Electron ( -1) mass = 1/1840
Neutron ( 0 ) mass= 1
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Is an atom charged?Is an atom charged?
• There are equal numbers of protons and electrons in an atom.
• An atom is an electrically neutral entity made up of a positively charged nucleus (protons and neutrons) with negatively charged electrons moving round the nucleus.
• There are equal numbers of protons and electrons in an atom.
• An atom is an electrically neutral entity made up of a positively charged nucleus (protons and neutrons) with negatively charged electrons moving round the nucleus.
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Different types of atomsDifferent types of atoms
• Atoms are different because they have different number of protons and electrons.
• Atoms of the same element contain the same number of protons and those of different elements contain different number of protons.
• Atoms are different because they have different number of protons and electrons.
• Atoms of the same element contain the same number of protons and those of different elements contain different number of protons.
79Au79Au
12Mg12Mg
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What is the atomic number?What is the atomic number?
• The atomic number is the number of protons that an element has in each atom.
• The atomic number is like the identification card number – each element has a unique atomic number.
• The atomic number is the number of protons that an element has in each atom.
• The atomic number is like the identification card number – each element has a unique atomic number.
12Mg12Mg
Atomic number
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The periodic tableThe periodic table• The elements in the periodic table are
arranged in order of increasing atomic number.
• The elements in the periodic table are arranged in order of increasing atomic number.
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Are there other ways of representing atoms?
Are there other ways of representing atoms?
• Atoms can be represented by circles, spheres or balls of different colours and sizes.
• Atoms can be represented by circles, spheres or balls of different colours and sizes.
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JournalJournalCarbon Oxygen Boron Sodium
Nucleon =mass Number 12 16 11 23
Proton Number 6 8 5 11
Number of protons 6 8 5 11
Number of electrons 6 8 5 11
Number of neutrons 12-6=6 16-8=8 11-5=6 23-
11=12
Practice
27
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ClassworkClasswork
• Workbk Pg 111-115a• Workbk Pg 111-115a
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What are ions?What are ions?• Ions are charged particles• An ion is formed when an atom loses or
gains electrons.
• Ions are charged particles• An ion is formed when an atom loses or
gains electrons.
Positive ion Negative ion
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Why do they gain or lose electrons?Why do they gain or lose electrons?
• To be like Group VIII elements• To be like Group VIII elements
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How are positive ions formed?How are positive ions formed?
• When an atom loses an electron,
It will have more positive charges than negative charges;
• It becomes a positive ion.
• [insert diagram of formation of Na+ from Pg 176]
• When an atom loses an electron,
It will have more positive charges than negative charges;
• It becomes a positive ion.
• [insert diagram of formation of Na+ from Pg 176]
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How are negative ions formed?How are negative ions formed?
• When an atom gains an electron,
It will have more negative charges than positive charges;
• It becomes a negative ion.
• [insert diagram of formation of Cl- from Pg 176]
• When an atom gains an electron,
It will have more negative charges than positive charges;
• It becomes a negative ion.
• [insert diagram of formation of Cl- from Pg 176]
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Bonding Bonding • And they live happily ever after• And they live happily ever after
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Overall process…Overall process…
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Formation of ionsFormation of ions• When atoms undergo ionic bonding, ions
are formed.• When atoms undergo ionic bonding, ions
are formed.
Atoms Ions
Ionic
Bonding
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Some common ionsSome common ions
• [Insert table of ions from Pg 177]• [Insert table of ions from Pg 177]
Valency Positively charged ions Negatively charged ions1 sodium
potassiumsilvercopper(I)hydrogen*ammonium
Na+ K+ Ag+ Cu+ H+ NH4
+
chloridebromideiodidehydroxidenitrate
Cl -
Br -
I -
OH -
NO3-
2 lead(II)copper(II)magnesiumcalciumzincbariumiron(II)
Pb2+
Cu2+
Mg2+
Ca2+
Zn2+
Ba2+
Fe2+
*sulfatesulfite*carbonateoxideSulfide
SO4 2-
SO32-
CO32-
O2-
S2-
3 iron(III)aluminium
Fe3+
Al3+
*phosphate PO4 3-
* Complex ions-important in upper secondary
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What are molecules?What are molecules?
• A molecule is made up of two or more atoms combined together.
• A molecule is made up of two or more atoms combined together.
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Molecules of elementsMolecules of elements
• Molecules of elements consist of a fixed number of the same type of atoms combined together.
• Molecules of elements consist of a fixed number of the same type of atoms combined together.
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Molecules of compoundsMolecules of compounds
• Molecules of compounds consist of a fixed number of two or more different types of atoms combined together.
• Molecules of compounds consist of a fixed number of two or more different types of atoms combined together.
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Metals tend to form positive ionsMetals tend to form positive ions
• Non-metals tend to form negative ions• Non-metals tend to form negative ions
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Do all compounds exist as molecules?Do all compounds exist as molecules?• No, not all compounds
exist as molecules
• Some compounds, such as sodium chloride, are formed by the attraction of ions.
• No, not all compounds exist as molecules
• Some compounds, such as sodium chloride, are formed by the attraction of ions.
Sodium chloride lattice
Ions
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Chemical formulaeChemical formulae
• The chemical formulae of a molecule shows the number and types of atoms it contains.
Examples• Oxygen is O2 and methane is CH4
• The chemical formulae of a molecule shows the number and types of atoms it contains.
Examples• Oxygen is O2 and methane is CH4
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Which of the following are elements and which are compounds?
Which of the following are elements and which are compounds?
• Name of molecule and Chemical formula].
• Name of molecule and Chemical formula].
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Picture referencesPicture references
• Democritus• http://www.stenudd.com/myth/greek/images/democritus_1628_Brugghen.jpg • John Dalton• http://cache.eb.com/eb/image?id=8421&rendTypeId=4 • J J Thomson• http://www.aip.org/history/electron/images/jj-equip.jpg • Niels Bohr• http://web.gc.cuny.edu/sciart/copenhagen/nyc/index.htm • Quantum Model• http://static.howstuffworks.com/gif/atom-quantum.jpg • Plum pudding• http://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Plum_pudding_atom.svg/348px-Plum_pudding_atom.svg.png • Rutherfod’s model• http://www.faqs.org/docs/qp/images/rfmodel.gif • Bohr’s model• http://csep10.phys.utk.edu/astr162/lect/light/bohrframe/bohr2.gif
• Democritus• http://www.stenudd.com/myth/greek/images/democritus_1628_Brugghen.jpg • John Dalton• http://cache.eb.com/eb/image?id=8421&rendTypeId=4 • J J Thomson• http://www.aip.org/history/electron/images/jj-equip.jpg • Niels Bohr• http://web.gc.cuny.edu/sciart/copenhagen/nyc/index.htm • Quantum Model• http://static.howstuffworks.com/gif/atom-quantum.jpg • Plum pudding• http://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Plum_pudding_atom.svg/348px-Plum_pudding_atom.svg.png • Rutherfod’s model• http://www.faqs.org/docs/qp/images/rfmodel.gif • Bohr’s model• http://csep10.phys.utk.edu/astr162/lect/light/bohrframe/bohr2.gif
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Picture referencesPicture references
• Atom• http://content.answers.com/main/content/wp/en/d/d8/Atom_diagram.png • STM• http://www.phys.unt.edu/stm/images/STM-side_view.JPG • Molecule – spheres of different colours • http://www.nrao.edu/pr/2004/GBTMolecules/molecules.JPG • Ball and stick model• http://www.lsbu.ac.uk/water/images/so4clust.jpg • Ions• http://www.chem.purdue.edu/gchelp/liquids/ions.gif • Air molecules• http://www.chemistryland.com/CHM107/AirWeBreathe/Comp/AirAtomsMolecules.jpg• Molecules of elements and compounds• http://www.eoearth.org/upload/thumb/2/24/Compounds_molecules.jpg/300px-Compounds_molecules.jpg • Sodium chloride lattice• http://www.rkm.com.au/imagelibrary/thumbnails/SALT-NaCl-2-150.jpg
• Atom• http://content.answers.com/main/content/wp/en/d/d8/Atom_diagram.png • STM• http://www.phys.unt.edu/stm/images/STM-side_view.JPG • Molecule – spheres of different colours • http://www.nrao.edu/pr/2004/GBTMolecules/molecules.JPG • Ball and stick model• http://www.lsbu.ac.uk/water/images/so4clust.jpg • Ions• http://www.chem.purdue.edu/gchelp/liquids/ions.gif • Air molecules• http://www.chemistryland.com/CHM107/AirWeBreathe/Comp/AirAtomsMolecules.jpg• Molecules of elements and compounds• http://www.eoearth.org/upload/thumb/2/24/Compounds_molecules.jpg/300px-Compounds_molecules.jpg • Sodium chloride lattice• http://www.rkm.com.au/imagelibrary/thumbnails/SALT-NaCl-2-150.jpg