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C2 revision topics 1 and 2 • To understand atomic structure • To be able to draw ions • To be able to explain ionic bonding and the tests for ions.
C2 revision topics 1 and 2
• To understand atomic structure
• To be able to draw ions
• To be able to explain ionic bonding and the tests for ions.
The elements, alone or in
combinations, make up our
bodies, our world, our sun, and in fact, the entire
universe!
Elements
The Periodic Table
Dmitri Mendeleev (1834 - 1907)
What do the squares mean?
Elements are organized on the table according to their atomic number, usually found near the bottom of the square.
The atomic number refers to how many protons an atom of that element has. The atomic number is unique to that element. No two elements have the same atomic number.
Alkali Metals
• They are the most reactive metals.
• They react violently with water.
• Alkali metals are never found as free elements in nature. They are always bonded with another element.
Transition Metals
• Transition Elements include those elements in the B families.
• These are the metals you are probably most familiar: copper, tin, zinc, iron, nickel, gold, and silver.
• They are good conductors of heat and electricity.
Halogen Family
• The elements in this family are fluorine, chlorine, bromine, iodine, and astatine.
• Halogens have 7 valence electrons, which explains why they are the most active non-metals. They are never found free in nature.
Halogen atoms only need to gain 1 electron to fill their outermost energy level. They react with alkali metals to form salts.
Noble Gases
• Noble Gases are colorless gases that are extremely un-reactive. • One important property of the noble gases is their inactivity.
They are inactive because their outermost energy level is full. • Because they do not readily combine with other elements to
form compounds, the noble gases are called inert. • The family of noble gases includes helium, neon, argon,
krypton, xenon, and radon. • All the noble gases are found in small amounts in the earth's
atmosphere.
• Atoms contain 3 particles.
• These are called sub-atomic particles.
• They are:
- protons - neutrons
- electrons
What does an atom look like?
Electrons move around the nucleus in shells.
Protons and neutrons exist in the centre of the atom, together they are called the nucleus.
What does an atom look like?
What does an atom look like?
Electrons have a negative charge.
Protons have a positive charge.
Neutrons are neutral.
How do we recognize each element?
• Each element has a specific number of protons, neutrons and electrons.
• This information can be found using the numbers that are on the periodic table.
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• The atom of any particular element always contains the same number of protons. E.g. – Hydrogen atoms always contain 1 proton – Carbon atoms always contain 6 protons – Magnesium atoms always contain 12 protons
• The number of protons in an atom is known as its atomic number.
• It is the smaller of two numbers shown in most periodic tables.
• It also tells us how many electrons can be found.
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What do the numbers mean?
• Mass is very important.
• It is the combined mass of protons and neutrons.
• Different for every element.
• Found in the Periodic table.
12
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What do the numbers mean?
Electrons exists in electron shells.
The electrons DO
NOT live in the nucleus with the
protons and neutrons.
They orbit the nucleus instead.
What about electrons?
• 1st electron shell = 2 electrons
• 2nd electron shell = 8 electrons
• 3rd electron shell = 8 electrons
• Electrons fill the first shell, then the second, then the third
How many electrons fit on each shell?
• N= • P= • E=
12
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• N= • P= • E=
12
C 6
X
X
X
X
X
X
2.4
Write the electron configuration for the following
• Lithium
• Magnesium
• Oxygen
• Calcium
• Sodium
• nitrogen
• 2.1
• 2.8.2
• 2.6
• 2.8.8.2
• 2.8.1
• 2.5
Two atoms of the same element.
They then found two atoms of the same element (like chlorine), that seemed to
have different masses!
They both looked like chlorine, smelled like chlorine, reacted in
a similar way….so they must have the
same number of protons and
electrons. They must be the same
element!
They solved the dilemma by calling these special atoms “ISOTOPES”, and realised that the difference in the mass must be caused by
the particle that contributes to mass, but is neutral, so does not affect
reactions!
Isotopes
• Isotopes have the same number of protons and electrons.
• Different number of neutrons.
• React in the same way due the same numbers of electrons and protons.
• They are the same element
An isotope is an atom with a different number of neutrons:
Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more.
Notice that the mass number is different. How many neutrons does each isotope have?
The relative atomic mass of oxygen is given as 16 in most
periodic tables. What does this infer about the abundance of the
difference isotopes of oxygen?
How do they work out the relative atomic mass
Why does Chlorine have a relative atomic mass of 35.5?
• (35 x 75/100) + (37 x 25/100)
• = 26.25 + 9.25
• = 35.5 Grade B
Alternative ways this question could be shown
• (35 x 75/100) + (37 x 25/100)
• = 26.25 + 9.25
• = 35.5 • (35 x 75) + (37 x 25)
100
• = 26.25 + 9.25
• = 35.5
Same answer
Alternative ways the question could be written
• The relative atomic mass of an element can be calculated from the relative abundances of its isotopes. For example, this is how you calculate the relative atomic mass of Chlorine, if 75% of it is 17
35 Cl and 1737 is Cl 25% :
Sample exam questions…. • November 2012 Foundation
Sample exam questions…. • November 2012 Higher
Exam question
• 2. Find nickel on the periodic table.
• (a) What name is given to metals in this part of the periodic table? (1)
•
• (b) What is the symbol for nickel? (1)
•
• (c) What is the atomic number of nickel? (1)
• (Total 3 marks)
•
• 5. Use the periodic table to answer the following questions.
• (a) Name an element in group 3 (1)
•
• (b) Name the metal with the symbol Co (1)
•
• (c) Give the symbol of the element chromium (1)
•
• (d) Name an element in the same period as sodium (1)
• (Total 4 marks)
• 6. Table salt contains sodium chloride.
• ‘Lo-salt’ is an alternative to table salt. It contains potassium chloride.
• (a) (i) What element is found in both sodium chloride and potassium chloride? (1)
•
• (ii) Give the symbol for an atom of this element. (1)
•
• (b) (i) In which group of the periodic table is sodium found? (1)
•
• (ii) In which group of the periodic table is potassium found? (1)
Work out the electrical charge of sodium atom.
Na 23
11
Let do this one together…
Vital Statistics of the atom Particle Charge Relative Mass
Protons +1 1
Neutrons 0 1
Electrons -1 1/1840
Work out the electrical charge of sodium atom.
Number of protons = 11 Total proton charge = +11
Number of electrons = 11 Total electron charge = -11
Number of neutrons = 12 Total electron charge = 0
Total overall electrical charge = +11 – 11 = 0
+
Sodium Chlorine
•Sodium is a metal reacting with a non-metal chlorine.
•The reaction occurs when two unstable atoms become stable atoms.
ALL atoms want a FULL outer shell of electrons! To achieve this they can give extra electrons
away or gain some more!
+
Sodium Chlorine
•The sodium atom loses 1 electron and chlorine gains one electron.
•This gives both atoms a full outer shell of electrons.
ALL atoms want a FULL outer shell of electrons! To achieve this they can give extra electrons
away or gain some more!
+
Sodium Chlorine
Start of the reaction End of the reaction
Electronic configuration
Sodium Chlorine
2,8,1 2,8,7
Sodium Chlorine
2,8 2,8,8
+
Sodium Chlorine
•Number of protons = 11
•Number of electrons = 10
•Overall charge = +11 – 10 = +1
•Number of protons = 17
•Number of electrons = 18
•Overall charge = +17 – 18 = -1
The sodium and chlorine particles formed are now called ions. The number of protons and electrons are not equal.
+
Sodium Chlorine
Na+ Cl- Known as a cation Known as an anion
Na
Cl
Na+
Cl-
+
-
This is called ionic bonding as the bonds that hold the charged atoms together are ionic bonds.
Na
Cl
Na+
Cl-
+
-
This is called ionic bonding as the bonds that hold the charged atoms together are ionic bonds.
Li
F
Li+
F-
+
-
+
Magnesium Oxygen
•Number of protons = 12
•Number of electrons = 10
•Overall charge = +12 – 10 = +2
•Number of protons = 8
•Number of electrons = 10
•Overall charge = +8 – 10 = -2
•The Mg atom loses 2 electrons to become Mg2+.
•The O atom gains 2 electrons to become O2-.
•They are attracted to each other using ionic bonds as they are oppositely charged.
Ionic compounds are made from bonding CATIONS with ANIONS
When writing the name of the
compound the cation ALWAYS
comes first.
NaCl
HCl Na+ Cl-
H+ Cl-
Common cations and anions
Stick this key table in your book… Where do you find cations on the periodic table? Where do you find anions on the periodic table?
How do we work out ionic compounds?
Ionic compounds are NEUTRAL. They have equal
numbers of positive and
negative charges.
NaCl
Na+ Cl- The net charge is 0
What about more complicated ionic compounds?
Aluminum is a cation and can be put together with
oxygen. Al3+ O2-
What about more complicated ionic compounds?
Aluminum is a cation and can be put together with
oxygen.
Al3+ O2-
The ionic compound must equal a charge of 0.
What about more complicated ionic compounds?
Aluminum is a cation and can be put together with
oxygen.
Al3+ O2-
Will this work? No – the overall charge is +1.
AlO
What about more complicated ionic compounds?
Aluminum is a cation and can be put together with
oxygen. Al2O3
Al3+ O2-
The net charge is 0
Use the following text to state how “chlorides” react and “nitrates” react.
C
•Sodium chloride is made up of a metal and a non-metal.
•This combination produces the particles ions.
In an ionic compound, millions and millions of ions are packed
together in a regular cubic arrangement,
joined by ionic bonds.
•This is called a giant ionic structure.
These ionic bonds are STRONG ELECTROSTATIC FORCES
The structure of the ionic lattice affects the properties of the ionic compound.
The ionic lattice will continue to build in this way until there are no more ions left to add.
•We can carry out an experiment.
•Two graphite electrodes are submerged in pure water and connected to a power pack and a bulb.
What do you expect to happen?
Electrodes
•The bulb does not light in water.
•This is because water does not contain any charged particles.
•There are no charged particles to carry the current.
Electrodes
•Now instead of using pure water lets use salt water.
What do you expect to happen?
Electrodes
•The bulb lights.
•The particles in the sodium chloride are charged particles (Na+ and Cl-).
•These charged particles carry the electricity.
Electrodes
What other properties do ionic substances have?
Property Explanation in terms of ions
Good electrical conductors when molten and dissolved in water.
Poor electrical conductors when solid.
Regular crystal shape.
High melting and boiling points.
When liquid (molten), the ions can break free of the lattice and are able to move. The ions are charged particles and so can carry an electric current.
As solids, ionic compounds cannot conduct electricity because their ions are bonded together in the lattice. ions in solid
state cannot move
ions in molten state can
move and conduct electricity
Ionic compounds are usually soluble in water because water molecules have a slight electrical charge and so can attract the ions away from the lattice. When dissolved, the ions are free to move and can carry an electric current.
Ionic compounds are brittle – they shatter when they are hit.
When the lattice is hit, a layer of ions is shifted so that ions with the same charges are lined up together.
These like charges repel each other and so split the ionic lattice causing it to shatter.
repulsion
force
Ionic bonds are strong, so why does this happen?
Why are ionic compounds solid at room temperature and have high melting points and boiling points?
Larger ionic charges produce stronger ionic bonds and so much more heat is required to break the ionic bonds in magnesium oxide than in sodium chloride.
sodium chloride
magnesium oxide
Compound Ion charges
Melting point (oC)
Boiling point (oC)
1+ and 1-
2+ and 2-
801 1,413
2,852 3,600
strong ionic bonds hold ions
together Ionic bonds are strong and a lot of heat is needed to break them.
Can we use better scientific language?
Soluble – a substance that dissolves well in another liquid.
Insoluble – a substance that does not dissolve in another liquid. Solubility – the amount of a substance that will dissolve.
When we look at ionic compounds and their solubility we have rules to follow.
Soluble in water Insoluble in water
All common sodium, potassium and ammonium salts
All nitrates
Most chlorides Silver chloride, lead chloride
Most sulfates Lead sulfate, barium sulfate, calcium sulfate.
Sodium carbonate, potassium carbonate and ammonium carbonate
Most carbonates
Sodium hydroxide, potassium hydroxide, ammonium hydroxide.
Most hydroxides
These reactions were called
precipitation reactions.
If one of the products of a chemical reaction is insoluble it will come out of the solution.
Lead nitrate and potassium iodide are salts that are both soluble in water.
Lead nitrate + potassium iodide lead iodide + potassium nitrate
This is a displacement reaction.
Potassium is more reactive than lead and therefore the potassium has displaced the lead
This equation could be written better…
Lead nitrate + potassium iodide lead iodide + potassium nitrate
State symbols can be used
(s) - solid
(l) - liquid
(g) - gas
(aq) – aqueous, dissolved in water
Lead nitrate (aq) + potassium iodide (aq) lead iodide (s) + potassium nitrate (aq)
Complete the word equation to make an insoluble salt
Magnesium sulfate + sodium carbonate ? + ?
Can you write the symbol equation?
Have you included state symbols?
Complete the word equation to make an insoluble salt
Magnesium sulfate + sodium carbonate Magnesium carbonate + sodium sulfate
MgSO4 (aq) + NaCO3 (aq) MgCO3 (s) + Na2SO4 (aq)
Lead nitrate and potassium iodide are salts that are both soluble in water.
Pb(NO3)2 (aq) + KI (aq) PbI2 (s) + KNO3 (aq)
Balance this equation
Lead nitrate (aq) + potassium iodide (aq) lead iodide (s) + potassium nitrate (aq)
Lead nitrate and potassium iodide are salts that are both soluble in water.
Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq)
Balance this equation
Lead nitrate (aq) + potassium iodide (aq) lead iodide (s) + potassium nitrate (aq)
A Put 1 cm depth of each of the cation solutions into six different test tubes.
B Add a few drops of sodium hydroxide solution to each test tube, and observe what happens.
C If a precipitate forms, add a further 1 cm of sodium hydroxide. Again observe any changes that might occur.
Practical – Testing for Cations
Cation Symbol Precipitate
Ammonium NH4+ (aq) none
Aluminium Al3+ (aq) White
Calcium Ca2+ (aq) White
Copper(II) Cu2+ (aq) blue
Iron(II) Fe2+ (aq) Green
How to make an insoluble salt
Sometimes we know what insoluble salt
we want make.
e.g. lead chloride for paint colour
To work out what reactants we need the following has to be thought about: a) A soluble salt with lead ions
b) A soluble salt with chloride ions.
c) Use the solubility laws (table) to
work out the reactants
HINT: ionic compounds are often called salts
How to make an insoluble salt
Sometimes we know what insoluble salt
we want make.
e.g. lead chloride for paint colour
To work out what reactants we need the following has to be thought about: a) A soluble salt with lead ions (lead
nitrate)
b) A soluble salt with chloride ions (sodium chloride)
Once the precipitate has been made it needs purifying as it is mixed with water.
Once the precipitate has been made it needs purifying as it is mixed with water.
Fireworks explode displaying a wide range of colours.
They explode with these colours as they contain a certain ionic
salt. Distress flares work in the same way!
The colour of the flame is specific to a particular metal ion.
Your task is to work out what colour some metal ions burn with and then use the results to determine what
the unknown samples are.
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• Dip the wire in a acid solution
• Hold the wire in Bunsen flame (to check if wire is clean)
• Place some of the salt on the wire
• Hold the salt in the flame
• Note the colour imparted to the flame.
• Wash the wire in acid.
• Repeat for other salts.
What do I do?
Flame tests are used to identify cations (positive ions).
Each metal ion burns with a different colour.
Anions are negatively charged and cannot be identified by flame tests.
Name 3 anions
Carbonates
What formula do carbonates have?
What ionic charge do they have?
CO3
CO32-
Carbonates can be tested for by decomposing it with hydrochloric acid. We can then test for one of the products.
What do you think this product might
be?
How do you think we will test for this
product?
Carbonates
Carbonates can be tested for by decomposing it with hydrochloric acid. We can then test for one of the products.
What do you think this product might
be? Carbon dioxide
How do you think we will test for this
product? If limewater goes milky
E.G.
Hydrochloric acid
calcium chloride
carbon dioxide
water Calcium carbonate
+ + +
• Add 1 spatula of a metal carbonate into a test tube.
• Half fill a second test tube with limewater
• Add 2 pipette full's of HCl into the test tube with the metal carbonate.
• Add the bung of the delivery into the top and place the straw of the delivery tube into the limewater.
• Note your observations
• Repeat for other carbonates.
What do I do?
Sulfates
What formula do sulfates have?
What ionic charge do they have?
SO4
SO42-
Sulfates can be tested for by adding dilute HCl and a few drops of barium chloride. A white precipitate is produced meaning that a sulfate is present.
Sulfates
E.G.
Barium chloride
sodium chloride
Barium sulfate
Sodium sulfate
+ +
Sulfates can be tested for by adding dilute HCl and a few drops of barium chloride. A white precipitate is produced meaning that a sulfate is present.
• Add a pipette full of sodium sulfate solution to a test tube.
• Add a pipette full of HCl and BaCl2
• If a white precipitate is made a sulfate is present.
What happens in the demo?
Chlorides
What formula do chlorides have?
What ionic charge do they have?
Cl
Cl-
Chlorides can be tested for by adding dilute nitric acid and silver nitrate solution. A white precipitate is produced meaning that a chloride is present.
Chlorides
E.G.
Silver nitrate
silver chloride
Sodium Nitrate
Sodium chloride
+ +
Chlorides can be tested for by adding dilute nitric acid and silver nitrate solution. A white precipitate is produced meaning that a chloride is present.
• Add a pipette full of sodium chloride solution to a test tube.
• Add a pipette full of nitric acid and silver nitrate solution.
• If a white precipitate is made a chloride is present.
What happens in the demo?
Exam questions – November 2012 Foundation
Exam questions – November 2012 Higher
