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COVALENT BONDING PRIMAS, MES, DOHA

COVALENT BONDING PRIMAS, MES, DOHA. Covalent compounds are formed when non-metal atoms react together. As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms.

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COVALENT BONDING PRIMAS, MES, DOHA

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  1. COVALENT BONDINGPRIMAS, MES, DOHA

  2. Covalent compounds are formed when non-metal atoms react together. As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms. The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells. Covalent compounds

  3. Covalent compounds are held together by this sharing of electrons. A pair of electrons shared in this way is known as a covalent bond. It is sometimes represented in full bonding diagrams (see figure 1). Often these bonds are just shown as a pair of electrons (xx) or even just a line (see figure 2). - Figure 1 Figure 2 F F X X F F Covalent bonds

  4. Sometimes just a few atoms join together in this way. This produces small covalent molecules – often known as simple molecular structures. a simple molecular structure covalent bonds Small covalent structures

  5. Sometimes millions of atoms are joined together by covalent bonds. This produces a rigid 3-D network called a giant lattice. a giant lattice covalent bonds Giant covalent structures

  6. The driving force for covalent bonding is again the attainment of outer electron shells that are completely full. This is achieved by sharing electrons where the shared electrons count towards the outer shells of both atoms. Sometimes this is achieved with equal numbers of each type of atom. Sometimes it is not! H H Cl H C Cl Cl N H H H H H Covalent bonding and electron structures

  7. Chlorine (2.8.7) needs 1 more electron to attain a full electron shell. Cl Cl Cl (2,8,7) (2,8,7) Cl (2,8,8) (2,8,8) Covalent bonding in chlorine Cl-Cl

  8. Both fluorine and chlorine needs 1 more electron to attain a full electron shell. Cl Cl F F (2,7) (2,8,7) (2,8) (2,8,8) Copy this diagram and add the electron arrangements that could exist in fluorine chloride (FCl).

  9. Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell. Cl Cl H (1) (2,8,7) H (2) (2,8,8) Covalent bonding in hydrogen chloride H-Cl

  10. Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more. Therefore, we need 2 hydrogens. O O H H H H H H O Covalent bonding in water

  11. Hydrogen (1) needs 1 more electron. H H H H H H H H C C 4 • How many does carbon (2.4) need? 4 • How many hydrogens per 1 carbon? • Draw bonding diagrams for CH4 (methane).

  12. Copy the atoms below. Complete the diagram showing how each atom can achieve full shells. H H O O O O H H

  13. Mostly electrons are shared as pairs. There are some compounds where they are shared in fours or even sixes. This gives rise to single, double and triple covalent bonds. Again, each pair of electrons is often represented by a single line when doing simple diagrams of molecules. Cl-Cl O=O N=N Double bond Triple bond Single bond Covalent bonding - multiple bonds

  14. Oxygen (2.8.6) needs 2 more electrons to attain a full electron shell. O O O O Covalent bonding in oxygen O=O 4 electrons

  15. Nitrogen (2.8.5) needs 3 more electrons to attain a full electron shell and forms a triple bond. Draw a bonding diagram of nitrogen. N=N N N N N 6 electrons

  16. Hydrogen fluoride (HF) Hydrogen sulphide (H2S) Ethane (C2H6 and the carbons are joined by a single covalent bond) Carbon dioxide (CO2 and the carbon oxygen bonds are double bonds) Draw ‘dot and cross’ type bonding diagrams for each of the following: H H F H O C O C C H H S H H H H

  17. Ionic compounds are very brittle. Opposite charges attract, so neighbouring ions are pulled together. When something hits the substance a layer of ions will be pushed so that they are next to ions with the same charge. Attraction becomes: Bonding and physical properties + + + + - - - - - - - - + + + + + + + + - - - - - + - + + + + - - - - + + + + + - + - + - This repulsion leads to breaking up of the lattice. hammer

  18. Covalent substances do not conduct electricity. This is because in covalent substances the outer electrons are fixed (localised) between specific atoms. Metals conduct electricity. In metals the electrons can, given a potential, move anywhere throughout the structure. Bonding and physical properties electrons fixed in covalent bonds H H C C H H electrons free to move H H

  19. Ionic substances do not conduct electricity as solids. When melted or dissolved they will conduct electricity. This is because the electricity is carried through the solution by the ions which are free to move when the ionic compound is molten or in solution. Bonding and physical properties + + - - - - + + + + + + - - - - + - - + - + + - - + + + - + Molten – mobile Does conduct Solid – not free to move Doesn’t conduct - + -

  20. Generally substances with giant structures have high melting points and boiling points. Small molecules have melting points and boiling points that increase as the size of the molecule increases. Bonding and physical properties In giant structures all the atoms are tightly bonded together. Usually they are high melting-point solids. + + - - Small molecules tend to be gas, liquid solids with low melting points. - - + + + + - - - + - weak forces between molecules + + - - + + + - + - + -

  21. Generally substances with giant structures do not dissolve easily (although many ionic compounds dissolve in water for a special reason). Again this is because in giant structures separating the particles involves breaking chemical bonds. Bonding and physical properties Giant structures generally don’t dissolve easily. + + - - Small molecules usually dissolve in a range of solvents. We just separate one molecule from another. - - + + strong bonds between the atoms/ions + + - - - + - weak forces between molecules + + - - + + + - + - + -

  22. The density of substances depends upon how closely the atoms are packed together. Giant structures, metals especially, tend to be dense because all atoms/ions are pulled tightly together. Small molecules often have lower densities. Bonding and physical properties Giant structures generally have high densities. + + - - Small molecules tend to have low densities because of space wasted between the molecules. - - + + atoms / ions held closely together + + - - - + - weak forces between molecules + + - - + + + - + - + -

  23. Which of the following will have covalent bonding? Sodium chloride Iron Bronze Nitrogen dioxide

  24. Which is a true statement about covalent bonds? Usually formed between metals and non- metals Involve transfer of electrons between atoms. Form full electron shells by sharing of electrons. Always involve 2 electrons per atom.

  25. Which of the following exists as a giant molecular structure? Water Carbon dioxide Sodium chloride Diamond

  26. What will be the formula of the compound formed by hydrogen and sulphur? HS H2S HS2 H2S2 1 H 1 32 S 16 2.8.6 1

  27. Which of these will conduct when liquid but not when solid? small molecules giant molecules metal ionic

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