Section 3 - Atoms, Elements and Compounds - With Notes Page

PAL (IGCSE) – CHEMISTRY Section 3 Atoms, Elements and Compounds

Atoms, Elements and Compounds

PAL (IGCSE) ChemistryRevision Book - Section 3

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Teacher: _________________________________

DIPONT Educational Resource – Science 1


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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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• 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



Treatment of cancer - the emitted radiation kills cancer cells



NOTES PAGE



• 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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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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• 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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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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Conduction in Ionic Materials

Solid

Melting

--

-

-

-

-

--

-

+

+

++

+

+

+

+

- +

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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• 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:



Weak bonds between the covalently bonded layers Layers can easily slide over each other – so suitable as a lubricant



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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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• 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

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

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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