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KS3 Science Quizzes

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docb4_72bond3 updated April 6th 2008

KS4 SCIENCE - Additional & Applied Chemistry help AQA GCSE Science - Chemistry CCEA GCSE Science - Chemistry Edexcel GCSE 360Science - Chemistry OCR GCSE 21st Century Science Suite - Chemistry  OCR GCSE Gateway Science Suite - Chemistry OCR GCSE Applied Science - Chemistry (double award) WJEC GCSE Science - Chemistry

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GCSE-IGCSE KS4 Science-CHEMISTRY and AS (basic) Chemistry Revision-Information Notes on

 The Structure and properties of substances - Ionic, Covalent & Metallic Bonding 

Part 1 Introduction - why do atoms bond together? & sub-index for Parts 2-5 (read 1st)

Part 2 Ionic Bonding - compounds and properties

Part 3 Covalent Bonding -small simple molecules and properties (this page)

Part 4 Covalent Bonding - macromolecules and giant covalent structures

Part 5 Metallic Bonding - structure and properties of metals



Part 3. COVALENT BONDING small simple molecules and properties

simple small molecule bonding e.g. water * physical properties of small molecules

inter/intra (internal)-molecular forces

Examples of covalent elements/compound examples described: hydrogen H2, chlorine Cl2, hydrogen chloride HCl, water H2O, ammonia NH3, methane CH4, oxygen O2, carbon dioxide CO2, ethene C2H4, nitrogen N2, ethane C2H6, chloromethane CH3Cl, methanol CH3OH

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(c) doc b3. Covalent Bonding - electron sharing in big or small molecules!

Covalent bonds are formed by atoms sharing electrons to form molecules. This type of bond usually formed between two non-metallic elements. The molecules might be that of an element i.e. one type of atom only OR from different elements chemically combined to form a compound.

The covalent bonding is caused by the mutual electrical attraction between the two positive nuclei of the two atoms of the bond, and the negative electrons between them.

One single covalent bond is a sharing of 1 pair of electrons, two pairs of shared electrons between the same two atoms gives a double bond and it is possible for two atoms to share 3 pairs of electrons and give a triple bond.

Note: In the examples it is assumed you can work out the electron configuration (arrangement in shells or energy levels) given the atomic number from the Periodic Table.

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(c) doc bThe bonding in Small Covalent Molecules

The simplest molecules are formed from two atoms and examples of their formation are shown below. The electrons are shown as dots and crosses to indicate which atom the electrons come from, though all electrons are the same. The diagrams may only show the outer electron arrangements for atoms that use two or more electron shells. The electron structures are given in (). Examples of simple covalent molecules are …


Example 1: two hydrogen atoms (1) form the molecule of the element hydrogen H2

(c) doc b and (c) doc b combine to form (c) doc b where both atoms have a pseudo helium structure of 2 outer electrons around each atom's nucleus. Any covalent bond is formed from the mutual attraction of two positive nuclei and negative electrons between them. The nuclei would be a tiny dot in the middle of where the H symbols are drawn! H valency is 1.


Example 2: two chlorine atoms (2.8.7) form the molecule of the element chlorine Cl2

(c) doc b and (c) doc b combine to form (c) doc b where both atoms have a pseudo argon structure of 8 outer electrons around each atom. All the other halogens would be similar e.g. F2, Br2 and I2 etc. Valency of halogens like chlorine is 1 here.


Example 3: one atom of hydrogen (1) combines with one atom of chlorine (2.8.7) to form the molecule of the compound hydrogen chloride HCl

(c) doc b and (c) doc b combine to form (c) doc b where hydrogen is electronically like helium and chlorine like argon. All the other hydrogen halides will be similar e.g. hydrogen fluoride HF, hydrogen bromide HBr and hydrogen iodide HI.

Note: Hydrogen chloride gas is a true covalent substance consisting of small HCl molecules. If the gas is dissolved in a hydrocarbon solvent like hexane or methylbenzene it remains as HCl molecules and because there are no ions present, the solution does not conduct electricity. However, if hydrogen chloride gas is dissolved in water, things are very different and the HCl molecules split into ions. Hydrochloric acid is formed which consists of a solution of hydrogen ions (H+) and chloride ions (Cl-). The solution then conducts electricity and passage of a d.c. current causes electrolysis to take place forming hydrogen and chlorine.

Reminder: How to work out formula of covalent compounds without going through some demanding electronic thinking is described on the "Elements, Compounds and Mixtures" page and it is followed by a section on naming compounds.

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Example 4: two atoms of hydrogen (1) combine with one atom of oxygen (2.6) to form the molecule of the compound water H2O

(c) doc b and (c) doc band (c) doc b combine to form (c) doc b so that the hydrogen atoms are electronically like helium and the oxygen atom becomes like neon. The molecule can be shown as (c) doc bwith two hydrogen - oxygen single covalent bonds (AS note: called a V or bent shape, the H-O-H bond angle is 105o). Hydrogen sulphide will be similar, since sulphur (2.8.6) is in the same Group 6 as oxygen. Valency of oxygen and sulphur is 2 here.


Example 5: three atoms of hydrogen (1) combine with one atom of nitrogen (2.5) to form the molecule of the compound ammonia NH3

three of (c) doc b and one (c) doc b combine to form (c) doc b so that the hydrogen atoms are electronically like helium and the nitrogen atom becomes like neon. The molecule can be shown as (c) doc b with three nitrogen - hydrogen single covalent bonds (AS note: called a trigonal pyramid shape, the H-N-H bond angle is 107o). PH3 will be similar since phosphorus (2.8.5) is in the same Group 5 as nitrogen. Valency of nitrogen or phosphorus is 3 here.

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Example 6: four atoms of hydrogen (1) combine with one atom of carbon (2.4) to form the molecule of the compound methane CH4

four of (c) doc b and one of (c) doc b combine to form (c) doc b so that the hydrogen atoms are electronically like helium and the nitrogen atom becomes like neon. The molecule can be shown as (c) doc b with four carbon - hydrogen single covalent bonds (AS note: called a tetrahedral shape, the H-C-H bond angle is 109o). SiH4 will be similar because silicon (2.8.4) is in the same group as carbon.

All the bonds in the above examples are single covalent bonds. Below are three examples 7-9, where there is a double bond in the molecule, in order that the atoms have stable Noble Gas outer electron arrangements around each atom. Carbon and silicon have a valency of 4.

More complex examples can be worked out e.g. involving C, H and O. In each case link in the atoms so that there are 2 around a H (electronically like He), or 8 around the C or O (electronically like Ne).


Example 7: (c) doc b Two atoms of oxygen (2.6) combine to form the molecules of the element oxygen O2. The molecule has one O=O double covalent bond (c) doc b. Oxygen valency 2.

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Example 8: (c) doc b One atom of carbon (2.4) combines with two atoms of oxygen (2.6) to form the compound carbon dioxide CO2. The molecule can be shown as (c) doc b  with two carbon = oxygen double covalent bonds (AS note: called a linear shape, the O=C=O bond angle is 180o). Valencies of C and O are 4 and 2 respectively.


Example 9: (c) doc b Two atoms of carbon (2.4) combine with four atoms of hydrogen (1) to form ethene C2H4. The molecule can be shown as (c) doc b with one carbon = carbon double bond and four carbon - hydrogen single covalent bonds (called a planar shape, its completely flat!, the H-C=C and H-C-H bond angles are 120o). The valency of carbon is still 4.

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Examples 10-13: The scribbles below illustrate some more complex examples. Can you deduce them for yourself? Ex. 10 nitrogen N2; Ex. 11 ethane C2H6; Ex. 12 chloromethane CH3Cl and Ex. 13 methanol CH3OH. Electronic origin of the diagrams showing the outer electrons of N, C, Cl and O: N at. no. 7 (2.5), H at. no. (1), C at. no. 6 (2.4), Cl at. no. 17 (2.8.7) and O at. no. 8 (2.6) plus a variety of crosses and blobs! The valencies or combining power in theses examples are N 3, H 1, C 4, Cl 1 and O 2. From these you can work out others e.g. Ex. 12 can be used to derive the ox diagram for tetrachloromethane CCl4.

(c) doc b

  • AS advanced level notes on shapes and bond angles:

    • Ex. 11 Ethane has a linked double tetrahedral shape, all H-C-H and H-C-C bond angles are 109o

    • Ex. 12 chloromethane has tetrahedral shape with  H-C-H and H-C-Cl bond angles of approximately 109o

    • Ex. 13 methanol, the four bonds around the central carbon are tetrahedrally arranged with a H 'wiggle' on the oxygen. All the H-C-H, H-C-O and C-O-H bond angles are approximately 109o

    • The blue icon e.g. below, represents an octahedral shape (e.g. SF6, complex transition metal ions like [Cu(H2O)6]2+ and the bond angles are either 90o or 180o

    • Simple molecules with a triple bond are often linear e.g. H-C(c) doc bC-H ethyne or H-C(c) doc bN hydrogen cyanide (methanenitrile)

    • The theory of shapes and bond angles with more examples and diagrams is on another page for AS-A2 students and with an extra section on bond angles in organic molecules.

  • on another web page is  how to work out a covalent formula given the element valencies (combining power)

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(c) doc bTypical properties of simple covalent substances - small molecules!

  • The electrical forces of attraction, that is the chemical bond, between atoms in a molecule are usually very strong, so,  most covalent molecules do not change chemically on moderate heating.

    • e.g. although a covalent molecule like iodine, I2, is readily vapourised on heating, it does NOT break up into iodine atoms I. The I-I covalent bond is strong enough to withstand the heating and the purple vapour still consists of the same I2 molecules as the dark coloured solid is made up of.

  • So why the ease of vaporisation on heating?

    • The electrical forces between individual molecules are weak, so the bulk material is not very strong physically and there are also consequences for the melting and boiling points.

  • These weak electrical attractions are known as intermolecular forces and are readily weakened further on heating. The effect of absorbing heat energy results in increased the thermal vibration of the molecules which weakens the intermolecular forces. In liquids the increase in the average particle kinetic energy makes it easier for molecules to overcome the intermolecular forces and change into a gas or vapour.  Consequently, small covalent molecules tend to be volatile liquids with low boiling points, so easily vapourised, or low melting point solids.

    • On heating the inter-molecular forces are easily overcome with the increased kinetic energy of the particles giving the material a low melting or boiling point and a relatively small amount of energy is needed to effect these state changes.

    • Energy changes for the physical changes of state of melting and boiling for a range of differently bonded substances are compared in a section of the Energetics Notes.

    • This contrasts with the high melting points of giant covalent structures with their strong 3D network.

    • Note: The weak electrical attractive forces between molecules, the so called intermolecular forces should be clearly distinguished between the strong covalent bonding between atoms in molecules (small or giant), and these are sometimes referred to as intramolecular forces (i.e. internal to the molecule).

  • Covalent structures are usually poor conductors of electricity because there are no free electrons or ions in any state to carry electric charge.

  • Most small molecules will dissolve in some solvent to form a solution.

    • This again contrasts with giant covalent structures where the strong bond network stops solvent molecules interacting with the particles making up the material.

  • The properties of these simple small molecules should be compared and contrasted with those molecules of a giant covalent nature (next section).

    • Apart from points on the strong bonds between the atoms in the molecule and the lack of electrical conduction, all the other properties are significantly different!

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ks4 national curriculum science examinations e-gcse-igcse chemistry revision *  ks4 national curriculum science examinations-gcse-igcse chemistry revision *  ks4 national curriculum  science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision * SITE PURPOSE EDUCATION - online learning or 'self-private-tuition' using revision notes, quizzes, practice tests involving GCSE Science CHEMISTRY in the areas of REVISING only the CHEMISTRY-Earth Science-Radioactivity at Doc Brown's Chemistry Clinic via HOMEPAGE in secondary school/schools, 6th form college/colleges, academy/academies or home self-study. Hopefully it will encourage interest and understanding of Chemistry, Earth Science and Radioactivity in any country of the world, though the site is written entirely in English. The website is designed to help and unofficially support students/teachers revise-learn/teach the chemistry for modular or co-ordinated examination science courses from UK QCA based AQA, OCR (Oxford and Cambridge) Twenty First (21st) Century and Gateway Science, Edexcel 360Science , Nuffield, Salters, Cambridge International (CIE), London International, WJEC, CCEA exams etc. Also, national award assessments-examinations for GCSE-IGCSE-KS4-O level-BTEC-NVQ applied, additional and chemistry national curriculum science courses. The notes should also provide some background theory for a coursework assignment or project. BUT please note that my on-line revision notes and quizzes are no substitute for good classroom teaching-lecturing and thorough studying of your own notes and textbooks, practicing past papers and a copy of the syllabus which are readily downloaded from the examination board sites, but I hope here and there they will lend a tutoring hand on some topic, unit, module etc. For final revision you have to be intellectually honest about what you don't know or follow, YOU have to take the stuff to pieces, analyse what you do/do not understand and reconstruct it so it all makes sense in the end. There is no other way, there are no magic secrets on how to revise and learn, its mainly down to hard work and just good old fashioned study and employing teach-yourself strategies without the need for extra tutors and tutoring lessons. I also think there is too much hit and miss revision using past papers (which I do NOT supply) and not enough systematic revision. I also hope it will help teachers in planning lessons and developing schemes of work for science-chemistry. There are no lesson plans on the site but there are plenty of quizzes to incorporate into classroom activities whether photocopied or on electronic whiteboard projector for use as self-tuition-assessment purposes and a variety of teaching and learning styles and the images may be used in Microsoft Word documents and powerpoint projections. The site seems to be used by a large number of home study tutors, particularly the revision notes. An individual tutor may print out the notes for science-chemistry learning teaching-tuition purposes and for background material for assignments and projects. I have no interest or time in producing WORD.doc or xxxx.pdf files of the notes at the moment. Neither have I time to write up many practical laboratory experiments ('lab'-'labs') at the moment, but the notes contain lots of background information of chemical reactions in terms of observations-balanced equations-reactants-products-theory etc. I also find it difficult to recommend specific exam websites or syllabus textbooks, it depends exactly on what you need, what you have time for, and there are so many of them to choose from and I do not supply past examination papers for classes. The sites resources include revision notes, quizzes and worksheets which provide support for home study or tuition for homework and coursework help e.g. science investigations for any of the key stage courses indicated, but I do not supply lesson plans. *  ks4 science examinations e-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision *  ks4 science examinations-gcse-igcse chemistry revision * Dr W P Brown Feb 15th 2008

useful alphabetical site indexdoc b's HOMEPAGE Site-Map for KS3 Science-GCSE-GCE-AS-A2-IB Chemistry

Online free help resources for Key Stage 4 AQA, Edexcel, OCR, CIE GCSE IGCSE BTEC Science, GCE, AS, A2 Advanced subsidiary Chemistry A levels, IB Diploma and US K12 (K-12 grades) courses and examinations and revising for the various syllabuses and specifications. Exploring the site for lessons, plans, ideas for projects and coursework, professional development. Through hard work the site has been built up over the course of many years with no need of special pc software except FrontPage and Hot Potatoes (uvic) for quizzes and worksheets. It is used in the classroom, home learning-tutoring-schooling and guidance, private tuition, school retakes revision. Whether you are a teacher/tutor teaching, a student studying, using the pages as self-study guides for your science-chemistry studies etc. etc. I hope the site supports your endeavour. 15-12-07 © Dr W P Brown

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KS3 Science Quizzes

GCSE KS4 Science-Chemistry

Advanced Level Chemistry

docb4_72bond3 updated April 6th 2008

KS4 SCIENCE - Additional & Applied Chemistry help AQA GCSE Science - Chemistry CCEA GCSE Science - Chemistry Edexcel GCSE 360Science - Chemistry OCR GCSE 21st Century Science Suite - Chemistry  OCR GCSE Gateway Science Suite - Chemistry OCR GCSE Applied Science - Chemistry (double award) WJEC GCSE Science - Chemistry

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