Types of interactions As a results of these interactions: 1. Strong interactions (chemical bonds: the attraction forces are extremely dominant over the repulsion forces) a) Ionic bonds b) Covalent bonds c) Metallic bond 1

Types of interactions 2. Weak interactions (physical bonds : the difference b/ the attraction & repulsion forces is slight 2. Weak interactions (physical bonds : the difference b/ the attraction & repulsion forces is slight) a) Van der Waals bonds a.1 Dipole-dipole a.2 Ion-dipol a.3 Induced dipole (Ion-induced dipole, dipole- induced dipole, London forces) b) Hydrogen bond 2

METALLIC BOND Metals tend to have high melting points and boiling points suggesting strong bonds between the atoms. Even a metal like sodium (melting point 97.8°C) melts at a considerably higher temperature than the element (neon) which precedes it in the Periodic Table. 3

Happens b/ atoms w/ low electronegativities. Metals have 1) Low I.E. 2) Many unfilled orbitals, making the valence electrons delocalized(shared by) amongst all the atoms and they are free to move throughout the metal. METALLIC BOND 4

Mobile sea of valence electrons Lattice of positive ions Mobile sea of valence electrons The attraction is b/ the positively charged metal ions and mobile electrons. 5

Metallic bonding in sodium The electrons can move freely within these molecular orbitals, and so each electron becomes detached from its parent atom. The electrons are said to be delocalised. The metal is held together by the strong forces of attraction between the positive nuclei and the delocalised electrons. 6

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Metallic bonding in sodium This is sometimes described as "an array of positive ions in a sea of electrons". If you are going to use this view, beware! Is a metal made up of atoms or ions? It is made of atoms. Each positive centre in the diagram represents all the rest of the atom apart from the outer electron, but that electron hasn't been lost - it may no longer have an attachment to a particular atom, but it's still there in the structure. Sodium metal is therefore written as Na - not Na + or potassium metal is written as K but not K +. 8

Metallic bond strength Depends on 1) Valence electron number of the metal 2) Atomic radii of the metal 9

In periodic table; Metallic bond strength increases Metallic bond strength decreases. 10

The physical properties of metals Melting points and boiling points Metals tend to have high melting and boiling points because of the strength of the metallic bond. Group 1 metals like sodium and potassium have relatively low melting and boiling points mainly because each atom only has one electron to contribute to the bond. They have relatively large atoms (meaning that the nuclei are some distance from the delocalised electrons) which also weakens the bond. 11

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The physical properties of metals Electrical conductivity Metals conduct electricity. The delocalised electrons are free to move Liquid metals also conduct electricity, showing that although the metal atoms may be free to move, the delocalisation remains in force until the metal boils. 13

Electrical conductivity of metals Animation showing electrons moving randomly and then the movement of electrons through a wire Animation showing electrons moving randomly and then the movement of electrons through a wire 14

Since the motion of electrons is easier compared to that of ions, metals are better conductors of electricity compared to ionic compounds. 15 Electrical conductivity of metals

Thermal conductivity Metals are good conductors of heat. Heat energy is picked up by the electrons as additional kinetic energy (it makes them move faster). The energy is transferred throughout the rest of the metal by the moving electrons. 16

Strength and workability Malleability and ductility Metals are described as malleable (can be beaten into sheets) and ductile (can be pulled out into wires). This is because of the ability of the atoms to roll over each other into new positions without breaking the metallic bond and the electron sea. 17

As metallic bond strength increases, the metallic activity decreases. 18

Because of the electron sea, metals have lustrous appearance since electrons can vibrate at the frequency of the light. This is also the basis for why the mirror image of an object is exactly the same w/ the object itself. 19

Transition metals Have also got covalent character along w/ the metallic character. As the number of unpaired electrons in d orbitals increases, the covalent character for the metal also increases. 20

21 V has 3 unpaired electrons and these electrons can overlap w/ other orbitals and make covalent bonds. Although Cr and Mn have bigger number of unpaired electrons, these electrons are not involved in covalent bond making because of having the spherical symmetry. From Mn to Zn, the number of unpaired electrons decreases and so does the melting point and hardness for the metals.

Transition metals Since Zn has all of its electrons paired, it has no covalent character, and hence, has the lowest melting point among all the 4 th period transition metals. 22