Chemistry GCSE (Unit 2) AQA

Unit 2 (additional chemistry) AQA Dual Core Science

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What are you expected to know?- Structures and bon

  • Atoms have a central nucleus. It is made up of protons with a positive charge and neutrons with no charge (negligible). The nucleus is surrounded by electrons with a negative charge, and are equal in number to the protons.
  • All atoms of an element have the same number of protons (= atomic number)
  • Atoms are arranged according to this atomic number.
  • Electrons are arranged in energy levels (shells). The pattern can be repesented by numbers (2, 8, 1) or dot and cross diagrams.
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What are you expected to know?- Structures and bon

  • They have similar chemical properties.

  • Ions are formed when atoms lose or gain electrons.

  • Ionic compounds are held together by strong attractions between oppositely charged ions in a giant structure.

  • Covalent bonds are formed when pairs of electrons are shared between atoms- & these substances form molecules.

  • Metals have giant structures of atoms 
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What are you expected to know?- Structures and bon

  • Elements in the same group in the periodic table have the same number of electrons in the highest energy level (outer shell).
  • The atoms (or positively charged electrons) are held together by delocalised electrons.
  • This allows metals to conduct heat and electricity.

  • The layers of atoms in metals can slide over each other.

  • This allows them to be bent and shaped. 
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Pre- test: Structures and bonding

1. What are the particles in an atom and in which part of an atom are they found?

2. What is the atomic number of an element?

3. How are electrons arranged in atoms?

4. What is special about the electron arrangement of elements in the same group in the periodic table?

5. What is special about the electron arrangement of the noble gases?


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Pre- test: Structures and bonding (cont.)

6) What happens to electrons when atoms of elements react?

7) What are ionic bonds?

8) Why does sodium chloride have the formula NaCl?

9) How are atoms arranged in metals?

10) How are the atoms within metals held in position within their giant structures?

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ATOMIC STRUCTURE- key points:

1. The nucleus of an atom is made of protons and neutrons.

2. Protons have a + charge, electrons have a - charge, and neutrons are not charged.

3. The atomic number of an element is the number of protons in the nucleus of its atoms.

4. Elements are arranged in order of their atomic number in the modern periodic table.

KEY WORDS: Protons, Neutrons, Electrons, Atomic Number, Proton Number, Periodic Table 

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Atomic Structure- CHECK YOURSELF QUESTIONS:

1. Name three types of pariticle in atoms.

2. What are the charges on the three particles?

3. How many electrons are there in an atom of magnesium (Mg)?

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THE ARRANGEMENT OF ELECTRONS IN ATOMS- key points:

1. Electrons in atoms are are in energy levels that can be represented by shells.

2. Electrons in the lowest energy level are in the shell closest to the nucleus.

3. Electrons occupy energy levels from the lowest first.

4. All the elements in a group of the periodic table have the same number of electrons in their highest energy level (outer shell).

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The arrangement of electrons in atoms-

  • Energy levels can be represented as shells, we can draw them as circles on a diagram, with electrons represented by dots or crosses. E.G. Calcium (2, 8, 8, 2)- 

(http://www.elthamhill.greenwich.sch.uk/websites/science_modular_revision/images/structure_and_bonding/struct33.gif)

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The arrangement of electrons in atoms- (cont.)

  • The lowest energy level (or first shell) can hold two electrons, and the second level (/shell) can hold eight.
  • Electrons occupy the lowest possible energy levels.
  • Therefore, the electronic structure of neon (with 10 electrons) is 2, 8, & Sodium (with 11 electrons) is 2, 8, 1.
  • ALL the elements in Group 1 have one electron in the highest energy level (/outer shell).
  • This shows that after each noble gas the next energy level begins to fill.

    KEY WORDS: energy level, shell, electronic structure. 

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The arrangement of electrons in atoms- CHECK YOURS

1. What are Electron shells?

2. What are the electronic structures of lithium, nitrogen and magensium in number form?

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CHEMICAL BONDING- key points:

1. Compounds are substances in which elements are chemically combined.

2. When elements react their atoms achieve stable arrangements of electrons.

3. Atoms gain or lose electrons to form ions or share electrons to form covalent bonds.

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Chemical Bonding-

  • The noble gases are unreactive because their atoms have stable arrangements of electrons.
  • Atoms of other elemtns can achieve stable electronic structures by gaining or losing electrons to form ions.
  • OR by sharing electrons to form covalent bonds.
  • When an elemtn in Group 1 reacts with an element in Group 7, an electron is transferred between atoms to form ions.
  • These ions have the electronic structures of noble gases. 
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Chemical Bonding- (cont.)

  • The atoms of elements in Group 1- lose their single outer electron.
  • E.G. Sodium, Na (2, 8, 1) forms sodium ions, Na+ (2, 8).
  • The atoms of elements in Group 7- gain one electron to form ions.
  • E.G. Chlorine, Cl (2, 8, 7) forms Chloride ions, Cl- (2, 8, 8).
  • Positive and negative ions attract and form ionic bonds.

    KEY WORDS: Ions, covalent bonds, ionic bonds, sharing, transferring. 

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Chemical Bonding- CHECK YOURSELF QUESTIONS:

1. Why are the noble gases unreactive?

2. What is the formula and electron arrangement for each of: a potassium ion, a magnesium ion, and an oxide ion?

3. Draw a dot cross diagram to show the formation of lithium fluoride.

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IONIC BONDING- key points:

1. Compounds mad of ions have giant structures that are very regular.

2. Strong forces of attraction act throughout the lattice to gold the ions together. 

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Ionic Boning-

  • Ionic bonding holds oppositly charged ions together in giant structures.
  • Strong electrostatic forces of attraction act in all directions.
  • Each ion in the lattice is surrounded by ions with the opposite charge so it held firmly in place.
  • The sodium chloride struture contains equal numbers of sodium ions and chloride ions- as shown by it formula= NaCl.
  • The sodium ions and chloride ions alternate to form a cubic lattice. 
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Ionic Boning- (cont.)

  • The ratio of ions int he formula and the structure of an ionic compound depend on the charges on the ions.

  • E.G. magnesium ions= Mg2+, and Chloride ions are Cl-, so the formula of magnesium chloride= MgCl2

  • Its structure contains twice as many chloride ions as magnesium ions.

    KEY WORDS: Giant structure, lattice, formula. 

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Ionic Boning- CHECK YOURSELF QUESTIONS:

1. What forced hold ions together in ionic bonding?

2. What does the formula NaCl tell you about sodium chloride?

3. What is the formula of calcium fluoride?

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Covalent bonding- KEY POINTS:

1. A covalent bond is formed when two atoms share a pair of electrons.

2. The number of covalent bonds an atom forms depends of the number of electrons it needs to achieve a stable electron arrangement.

3. Many covalently bonded substances consist of small molecules, but some have giant structures.

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Covalent Bonding-

  • The atoms of non-metals need to gain electrons to achieve stable arrangements of electrons.

  • They can do this by sharing electrons with other atoms.

  • Each shared pair of electrons strongly attracts the two atoms, forming a 'covalent bond'.

  • Atoms if elements in Group 7 need to gain one electron and so form a single covalent bond. 

  • Those in Group 6 need to gain two electrons and so form two covalent bonds. 
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Covalent Bonding- (cont.)

  • Atoms of elements in Group 5 form three bonds and those in Group 4 form four bonds.
  • Covalent bonds act only between the two atoms they bond.
  • Many covalently bonded substances consist of small molecules.
  • Some atoms that can form several bonds (e.g. Carbon), can join together to form giant covalent structures. 
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Covalent Bonding-

By choosing how we represent a covalent compound, we can show the outer energy level, the shared electrons, or just the fact that there are a certain number of covalent bonds:

(http://www.istockphoto.com/file_thumbview_approve/7862041/1/7862041-chemical-symbol-of-water-on-blackboard.jpg)        or       (http://www.askmehelpdesk.com/attachments/a/27026d1259677419-dot-cross-diagram-h2o2-test.png?stc=1)or    (http://www.bbc.co.uk/schools/gcsebitesize/science/images/diag_water.gif) or (http://img.wikinut.com/img/b1k_eya85ghsj8kw/jpeg/180x300/Water-Covalent-Bond.jpeg)

KEY WORDS: Sharing, covalent bond, molecules, giant covalent structures.

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Covalent Bonding- CHECK YOURSELF QUESTIONS:

1. What is a covalent bond?

2. How many covalent bonds can a silicon atom form?

3. Draw a dot and cross diagram for a molecule of ammonia.

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BONDING IN METALS- key points:

1. Metals have giant structures of layers of atoms arranged in a regular pattern.

2. The electrons in the highest energy level delocalise. This results in strong electrostatic forces between these electrons and the positively charged metal ions, holding the metal together.

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Bonding in metals-

  • The atoms in a metallic element are all the same size.
  • They form giant structures in which layers of atoms are arranged in regular patterns.
  • Although you cannot see individual atoms, you can see metal crystals on the surfaces of some metals.
  • You can grow metal crystals by displacement reactions.
  •  You can make models of metal structures by putting lots of small spheres like marbles together.
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Bonding in metals- (cont.)

  • When metal atoms pack together the electrons in the highest energy level (i.e. the outer shell electrons)- delocalise and move from one atom to another.
  • This produced positive ions in a 'sea' of moving electrons.
  • The delocalised electrons strongly attract the positive ions and hold the structure together.

    KEY WORDS: Crystals, delocalise. 

    (Exam tip: make it clear when answering in an exam that metallic bonding is strong and involves electrostatic forces).

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Bonding in metals- CHECK YOURSELF QUESTIONS:

1. How are the atoms arranged in metal crystals?

2. Where can you see metal crystals?

3. What are delocalised electrons?

4. What forces hold metal atoms in place in their giant structures?

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C2 1- End of chapter questions:

1. Why are the numbers of protons and electrons equal in an atom?

2. How many protons and electrons are in an atom of fluorine?

3. What is the arrangement of electrons in an atom of potassium?

4. What is special about the arrangement of electrons of the elements in Group 1?

5. What do we mean by a 'noble gas'?


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C2 1- End of chapter questions: (cont.)

6. Explain what happens when a sodium atom reacts with a fluorine atom.

7. What holds the ions together in an ionic lattice?

8. Potassium chloride is an ionic compound with formula KCl. What does its formula tell you about the structure of potassium chloride?

9. How is the number of covalent bonds that an atom can form related to its group in the periodic table?

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C2 1- End of chapter questions: (cont.)

10. Draw a diagram to show the bonds in hydrogen sulphide, H2S.

11. How are the atoms arranged in a metal crystal?

12. How are the atoms held in position in a metals giant structure?

END OF C2 (Chemistry Unit 2- Additional) 1

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Comments

viva123

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it would have been better if it was somebody actually reading it, not a fan of the audio, it's too robotic, but brill notes! :) 

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