Electrons responsible for the chemical properties of atoms Electrons in the outer energy level Valence electrons are the s and p electrons in the

Transcription

1

2 Electrons responsible for the chemical properties of atoms Electrons in the outer energy level Valence electrons are the s and p electrons in the outermost, or highest energy level The number of Valence electrons is given by the A Group name (1A, 2A 3A, 4A )

3 So the Valence Electrons are as follows: Group 1A- 1 valence electron, s 1 Group 2A- 2 valence electrons, s 2 Group 3A- 3 valence electrons, s 2 p 1 Group 6A- 6 valence electrons, s 2 p 4 Group 7A- 7 valence electrons, s 2 p 5 Group 8A- 8 valence electrons, s 2 p 6

4 Atoms will lose or gain electrons to complete the OCTET of electrons Atoms will lose or gain electrons to have filled valence s & p orbitals, or the electron configuration of the nearest noble gas Metals will lose electrons to become CATIONS Nonmetals will gain electrons to become ANIONS

5 Remember, a Lewis Dot structure is written as follows: Write the symbol Put one dot for each valence electrons Don t pair up until they have to (Hund s Rule)

6 Metals lose electrons to attain noble gas configuration Electron configuration makes sense to lose electrons Ca 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 (2 valence e-) Ca 2+ 1s 2 2s 2 2p 6 3s 2 3p 6 a noble gas configuration

7 Metals will have few valence electrons (usually 3 or less) These valence electrons are lost, creating a positive-charged ion Ca +2

8 Nonmetals gain electrons to attain noble gas configuration, making negative ions (anions S 1s 2 2s 2 2p 6 3s 2 3p 4 (6 valence e-) S 2-1s 2 2s 2 2p 6 3s 2 3p 6 a noble gas configuration

9 Nonmetals will have many valence electrons (usually 5 or more) They will gain electrons to fill outer shell

10 Ionic bonds are formed through the TRANSFER OF ELECTRONS Electrons are transferred to achieve NOBLE GAS FORMATION The resulting anions and cations are held together by opposite charges Ionic compounds are called SALTS Simples ratio of ionic compounds are called FORMULA UNITS

11 Write the Ionic combinations & Lewis Dot Structures of the Ionic Molecules for the following combinations: Ba + Cl Al + O K + Br Li + N

12 CRYSTALLINE structure, usually solids A regular, repeating arrangement of ions in the solid

13 Ions are STRONGLY bonded together The Crystalline Structure is rigid, with long-range order Hardness & Density are related to crystal composition and structure of the solid; i.e. how much space is between the ions in the crystal lattice These structures tend to melt at Specific & High melting points Amorphous solids are those that do not have an orderly arrangement

14 Conducting electricity is allowing charges to move In a solid, the ions are locked in place Ionic solids are insulators When melted, the ions can move around Melted ionic compounds conduct NaCl must get to about 800 o C Dissolved in water they conduct (aqueous)

15 What do Crystalline Solids look like?

16 How are atoms held together in a metallic solid? Metals have low ionization energies, and have a weak hold on their valence electrons? These outer electrons easily move around, as they do not belong to any one atom, but are part of the whole metal crystal

17 These outer electrons easily move around, as they do not belong to any one atom, but are part of the whole metal crystal The negatively charged electrons act as a cement that hold the positively charged metal ions in their relatively fixed positions.

18 Hammered into shape (bend) Also ductile- drawn into wires Both malleability and ductility explained in terms of the mobility of the valence electrons

19

20 Electrons allow atoms to slide by

21

22 Strong repulsion breaks crystals apart

23 We use lots of metals every day, but few are pure metals Alloys- mixtures of 2 or more elements, at least 1 is a metal Made by melting a mixture of the ingredients, then cooling Brass: an alloy of Cu and Zn Bronze: Cu and Sn

24 Properties often superior to just the element Sterling Silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware Steels are very important alloys Corrosion resistant, ductility, hardness, toughness, cost

25 Substitutional alloy- atoms in the components are about the same size Interstitial alloy- the atomic sizes are quite different; smaller atoms fit into the spaces between larger atoms

26 Ionic bonds occur between two elements whose electronegativity (E) difference is greater than 2.0 electrons are transferred from the metal to the nonmetal, creating oppositely charged ions which are then attracted. For bonds where the electronegativity difference is 1.0 to 2.0, a very polar covalent bond is formed, where a pair of bonding electrons are shared, but predominantly hang out around the more electronegative nonmetal atom. This creates a slightly negative nonmetal atom, and a slightly positive metal atom within the bond. For those bonds the E difference is 0.4 to 1.0, a moderate covalent bond is formed, creating slightly a negative nonmetal atom and a slightly positive metal atom. For bonds with difference in E, the bond is said to be NONPOLAR Covalent, where the bonding pair of electrons are shared EQUALLY.

27 Electronegativity Differences and Bond Types Electronegativity Difference Type of Bond Nonpolar Covalent Moderately Polar Covalent Very Polar Covalent Example H H (0) H Cl (0.9) H F (1.9) > 2.0 Ionic Na + Cl - (2.1)

28