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.

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.

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.

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.

Use your imagination!Use your imagination!

1803, John Dalton1803, John Dalton In 1897, JJ ThomsonIn 1897, JJ Thomson

Use your imagination!Use your imagination!

1911, Ernest Rutherford1911, Ernest Rutherford 1915, Niel Bohr1915, Niel Bohr

Present your drawingPresent your drawing

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.”

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”

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.”

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.”

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.”

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.”

Dalton’s modelDalton’s model

• Small solid spherical ball

• Small solid spherical ball

Thomson’s modelThomson’s model

• Electrons distributed among a continuous mass of positive charges

• Electrons distributed among a continuous mass of positive charges

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

Niel BohrNiel Bohr

• Electrons move round the nucleus in fixed orbits

• Electrons move round the nucleus in fixed orbits

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

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.

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

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.

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

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

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.

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.

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

ClassworkClasswork

• Workbk Pg 111-115a• Workbk Pg 111-115a

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

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

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]

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]

Bonding Bonding • And they live happily ever after• And they live happily ever after

Overall process…Overall process…

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

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

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.

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.

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.

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

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

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

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].

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

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