Chemical Bonding link link Problems and questions — What kind of bonds hold substances together? What kind of bonds hold substances together? What other forces are involved? What other forces are involved? ● How are the physical properties of compounds related to the nature of their chemical bonds? Electrons in the outermost energy level, which are involved in chemical bonding, are known as valence electrons. Since atoms are more stable when their outer energy level is filled, they tend to lose, gain, or share electrons to complete their outer energy level.

Valence Electrons Number of valence electrons of a main (A) group atom = Group number B has 3 valence electrons B has 3 valence electrons

Electronegativity Difference ● If the difference in electronegativities is between: ● 1.7 to 4.0: Ionic ● 0.3 to 1.7: Polar Covalent ● 0.0 to 0.3: Non-Polar Covalent Example: NaCl Na = 0.9, Cl = 3.0 Difference is 2.1, so this is an ionic bond!

Ionic Bonds link Ionic Bonds link link Ionic Bonds link Ionic Bonds link link ● An ionic bond is when electron(s) are transfered ● Some elements have outer shells that are almost empty; these elements tend to lose their electrons. Other elements have outer shells that are mostly full; these elements tend to hold on to their electrons and attract electrons from other atoms. When an atom gains electrons, a negatively charged atom—a negative ion—is created. Conversely, when an atom loses electrons, a positive ion is created. The oppositely charged ions attract one another, creating an ionic bond. Ionic compounds are usually between metals and nonmetals (opposite ends of the periodic table)

The properties of giant ionic structures are as follows. PropertyReason High melting and boiling points The electrostatic forces between ions are very strong and alot of energy is required to break up the lattice. Very poor electrical conductivity as a solid. But very good when molten or dissolved. As a solid the conductivity is very poor because the electrons are all in a fixed position and cannot transfer charge. However, when molten or dissolved the electrons are free to move. When dissolved the lattice separates into its charged ions: mobile charge carriers.

ionic and metallic compounds tend to have high melting points— The physical properties of compounds are related to the nature of their chemical bonds

Covalent Bonds link link ● A covalent bond occurs when electrons are shared between 2 atoms. ● Forces hold the atoms in a position where they are effectively stuck together and bonded through their shared valence electrons. ● the forces between molecules in covalent compounds are relatively weak, covalent compounds generally have low melting points

BF 3 SF 4

Spiderman exists only in movies ! Satae Seta Spatulae But Seriously, can we possibly make the Spiderman costume? The Gecko’s ability to walk on walls is NOT due to the (mis)understood vacuum theory: It is due to van der Waals attractive forces between spatulae (1 billion) on the Gecko’s leg and the wall

● This is why oil and water will not mix! Oil is nonpolar, and water is polar. ● The two will repel each other, and so you can not dissolve one in the other Bond Polarity