Ionic and Covalent Bonding 1

Bonding Atoms with unfilled valence shells are considered unstable. Atoms will try to fill their outer shells by bonding with other atoms. The number of valence electrons will determine how many bonds the atom can form. Two types of bonds we will discuss: –Ionic bonds –Covalent bonds 2

Ions Review Ions are charged atoms (positive or negative). Ions are formed when atoms gain or lose electrons. Positive ions are called cations. –Formed when the atom loses electrons. Negative ions are call anions. –Formed when the atom gains electrons. 3

Ionic Bonds Ionic bonds are formed between metals and non-metals. Ionic bonds are formed between oppositely charged atoms (ions). Ionic bonds are formed by the transfer of electrons. –One atom donates electrons to the other. 4

Ionic Bonds (continued) In an ionic bond one atom will lose its electron(s) and the other will gain them. –Depends on the number of valence electrons. The transfer of electrons creates a positive ion and a negative ion. The opposite charges attract one another, causing a bond to form. Bonding Animation 5

Drawing Ionic Bonds We can illustrate ionic bonding using Lewis structures. 1 – Draw the Lewis structure for each element. –Ex:NaCl 2 – Draw arrows to show the gain/loss of electrons 6

Drawing Ionic Bonds (continued) 3 – Draw ion Lewis diagrams showing the new charge for each ion. –Ex: The chemical formula for the compound formed represents the ratio of negative ions to positive ions. –Ex: NaCl – for every 1 sodium ion, there is also 1 chlorine ion. 7

Practice Drawing Ionic Bonds Elements Lewis Ion Lewis Formula Diagram Diagram Calcium Sulfur Magnesium Bromine Aluminum Oxygen 8

Covalent Bonds Covalent bonds form between two non- metals. Covalent bonds are formed when atoms share electrons. –Both atoms need to gain electrons, so they share the electrons they have. Atoms can share more than one pair of electrons to create double and triple bonds. 9

Covalent Bonds (continued) Atoms can share their electrons equally or unequally. When atoms share electrons equally it is called a non-polar bond. –Non-polar covalent bonds form between atoms of the same type. Ex: H 2 When atoms share electrons unequally it is called a polar covalent bond. –One atom pulls the electrons closer to itself. –The atom that pulls the electrons more gets a slightly negative charge. –The other atom gets a slightly positive charge. Ex: Water molecule Bonding Animation 10

Drawing Covalent Bonds We can illustrate covalent bonding using Lewis structures. 1 – Draw a Lewis structure for each element. –Ex: CH 2 – Draw circles around the shared pair(s) of electrons. –Ex: 3 - Continue adding atoms until all atoms have a full valence shell. –Ex: 11

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Practice Drawing Covalent Bonds ElementsLewisFormula Diagram Hydrogen Carbon Oxygen 13

Ionic Vs. Covalent Bonds Ionic Bonds Form when electrons are exchanged between atoms. Form between a metal and a non- metal. Covalent Bonds Form when electrons are shared between atoms. Form between two non-metals. Both types of bonds result in all atoms having a full outer energy level. 14