PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
Atoms, Elements and Compounds
PAL (IGCSE) ChemistryRevision Book - Section 3
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
Syllabus Content_______________________________
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
Syllabus Details________________________________
3. Atoms, elements and compounds3.1 Atomic structure and the Periodic TableCore• State the relative charges and approximate relative masses of protons, neutrons and electrons
Protons Neutrons ElectronsRelative Mass 1 1 1/2000Charge +1 Neutral -1
• Define proton number and nucleon number
Nucleon Number (Mass Number) = Number of protons and neutrons in the nucleus
Proton Number (Atomic Number) = Number of protons in the nucleus
Nucleus: Protons + Neutrons
The Atom
Electrons
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
• Use proton number and the simple structure of atoms to explain the basis of the Periodic Table (see section 9), with special reference to the elements of proton number 1 to 20
Period table• Structure based on Proton Number• Elements ordered by increasing PROTON NUMBER
• Define isotopes
Isotopes: Elements with the same number of protons but different numbers of neutrons
Example. Carbon 12 – 6 protons + 6 neutronsCarbon 14 – 6 protons + 8 neutrons
• State the two types of isotopes as being radioactive and non-radioactive
Two types of isotopes…
Radioactive – will decay to give a new element + an orparticleNon - radioactive – doesn’t decay
• State one medical and one industrial use of radioactive isotopes
Industrial Usage
Gamma Sourceunsterilised sterilised
Food Sterilization
Hydraulicram
detector
Beta Source
Quality Control
Sheet metal
Electronic instructionsto adjust rollers.
Food sterilization to prolong shelf life Quality control – measuring the thickness of materials in production
Medical Usage
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
Treatment of cancer - the emitted radiation kills cancer cells
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
• Describe the build-up of electrons in ‘shells’ and understand the significance of the noble gas electronic structures and of valency electrons (the ideas of the distribution of electrons in s and p orbitals and in d block elements are not required.) Note: a copy of the Periodic Table, as shown in the Appendix, will be available in Papers 1, 2 and 3)
Electron Configuration
Electron configuration up to 20 electrons
1st2nd
3rd4th
Nucleus
ElectronsShells
1st Shell: 2 electrons2nd Shell: 8 electrons3rd Shell: 8 electrons4th Shell: 2 electrons
Noble gas electron structure: The most stable configuration of electrons when bonding
Valence electrons: The electrons in the outer shell
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
3.2 Bonding: the structure of matterCore• Describe the differences between elements, mixtures and compounds, and between metals and non-metals
Element: Consists of only one type of atom
Mixture: Easily separated No chemical bonds between different parts of the mixture Properties of mixtures are a mixture of the properties of the
separate partsCompound:
Two or more elements Chemically bonded Very difficult to separate into original components Properties of compounds are completely different to their
original elementsMetals:
Shiny Good conductors of heat and electricity Metallic bonding
Non-Metals: Don’t conduct electricity (except carbon – graphite) Dull Poor conductors of heat
Elements
Mixture
Compounds
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
• Describe an alloy, such as brass, as a mixture of a metal with other elements
ALLOYS: Mixtures of metal with other elements
EXAMPLES: Steel = Iron + Carbon Bronze = Copper + Tin Solder = Tin and Lead Brass = Copper + Zinc
3.2 (a) Ions and ionic bondsCore• Describe the formation of ions by electron loss or gain
Ion Formation
Cl
Na
+
Cl-
Na+
+
Gaining Electrons
Losing Electrons
• Describe the formation of ionic bonds between elements from Groups I and VII
Ionic Bonding
Cl
Na
x
Cl
Na
x
+
-
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
3.2 (b) Molecules and covalent bondsCore• Describe the formation of single covalent bonds in H2, Cl2 , H2O, CH4 and HCl as the sharing of pairs of electrons leading to the noble gas configuration
Covalent Bonding
Cl Cl
Chlorine Gas: Cl2
1 pair of shared electrons = single covalent bond
H H
Hydrogen Gas: H2
1 pair of shared electrons = single covalent bond
xxx
xxxx x
Methane Gas: CH4
4 pairs of shared electrons =4 x single covalent bond
C H
H
H
H
O
HH
Water: H2O
2 pairs of shared electrons =2 x single covalent bond
x
x
x
x
Cl x H
1 pair of shared electrons =1 x single covalent bond
Hydrochloric Acid: HCl
• Describe the differences in volatility, solubility and electrical conductivity between ionic and covalent compounds
Property Ionic compound Covalent compoundVolatility Very low Normally highSolubility Soluble in water Normally insoluble in
water Electrical conductivity Conduct when molten or
in solutionInsulators
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
Conduction in Ionic Materials
Solid
Melting
--
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-
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+
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+
- +
Ions fixed in PositionIons can NOT moveCan NOT conduct Electricity
Ions FREE to moveCAN conduct electricity
MoltenDissolving-
- -
--
+
+
+
+
+
- +HO
H
HO
H
H
OH
Solution
Supplement• Describe the formation of ionic bonds between metallic and non-metallic elements
Ionic Bonding
O
Mg x
O
Mg
x
2+
2-
x
x
METAL
NON-METAL
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
• Describe the lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions
Ionic Giant Structure
-ve ion (e.g. Cl-)
+ve ion (e.g. Na+)
Metal
Non-metal
3.2 (c) MacromoleculesCore• Describe the giant covalent structures of graphite and diamond
Giant Covalent Structures
GraphiteDiamond
• Relate their structures to the use of graphite as a lubricant and of diamond in cutting
Diamond: One giant covalent structure with very strong bonds between all carbon
atoms Very hard substance – so suitable for cutting
Graphite:
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
Weak bonds between the covalently bonded layers Layers can easily slide over each other – so suitable as a lubricant
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
Supplement• Describe the electron arrangement in more complex covalent molecules such as N2, C2H4, CH3OH and CO2
C
H
Ethene: C2H4
H
HH
CC H
H
H
H
x
x
x
x
O
Methanol: CH3OH
C
Carbon Dioxide: CO2
x O
x
O xx
N N
Nitrogen Gas: N2
xx xxx
• Describe the macromolecular structure of silicon(IV) oxide (silicon dioxide)
Silicon (IV) Oxide (Silicon Dioxide)
Silicon (IV) oxide: Giant covalent structure Each silicon or oxygen atom bonded to a number of other atoms Substance is hard
3.2 (d) Metallic bonding Supplement• Describe the similarity in properties between diamond and silicon(IV) oxide, related to their structures
Similar properties Very high melting point Very hard
Similar structure Giant covalent
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PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds
• Describe metallic bonding as a lattice of positive ions in a ‘sea of electrons’ and use this to describe the electrical conductivity and malleability of metals
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Metals GIANT Structure
Metal Atoms (+ve ions)
Free electrons (-ve)
Conduction in Metals: Free electrons (sea of electrons) surround the metal lattice
structure These electrons are free to move when a potential difference is
applied Metals are therefore good conductors of electricity
Malleability of metals: Metals are very malleable – they can be easily rolled into thin
sheets This is because the regular array of metal atoms can easily slide
over one another
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