An antenna is a device to transmit and/or receive electromagnetic waves. An antenna must be tuned (matched) to the same frequency band as the radio system to which it is connected, otherwise reception and/or transmission will be impaired. Most cell phone antennas are as long as ¼ the wavelength of the wave they are transmitting or receiving. Your cell phone (usually) operates at a range of frequencies around 1900 MHz. What is the length (in cm) of the antenna in your phone?

18.The octet rule tells us that in every chemical reactions, elements will either gain or lose electrons to attain the noble gas electron configuration. This stable electron configuration is known as the octet configuration since it is composed of 8 valence. Oxygen’s electron configuration is 1s2 2s2 2p4. So when oxygen reacts with other elements to form compounds, it completes the octet configuration by taking 2 electrons from the element it reacts with

19. Actually pure metals are made up not of metal atoms but rather of closely packed cations (positively charge particles). These cations are then surrounded by a pack of mobile valence electrons which drift from one part of the metal to another. This is called metallic bond.

20. This is the energy which is needed to break a single bond. When the dissociation energy is large, this means that the compound is more stable. Since carbon to carbon bonds have high dissociation energy, therefore they are not very reactive.

21. Network solids are type of solids in which the atoms are covalently bonded to one another, so they are very stable. It takes higher temperature to melt them because breaking these covalent bonds required greater energy. Some examples are:
- Diamond
-Silicon Carbide