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<span> 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</span> 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<span> to
another. This is called metallic bond.</span>
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
<span>-Silicon Carbide</span>
Answer:
Number of neutrons: 44
Number of protons: 34
Number of electrons: 36
Explanation:
The atomic number of Se (Selenium) is 34
Mass number is 78
Number of neutrons = mass number - atomic number = 78 - 34 = 44
Number of protons is the same as the atomic number
Number of protons = 34
Selenium ion has a charge of -2. This means it accepts two more electrons
Number of electrons = atomic number + 2 = 34 + 2 = 36
According to the report of US Environmental Protection
Agency, majority of large dose radiation exposure comes from natural background
radiation sources particularly the radioactive gases radon and thoron. This two
gases form when naturally occurring elements decay. However in the case of
man-made sources, the largest dose comes from medical x-rays.
10 HSiCl3+ 15 H2O→H10Si10O15+ 30 HCl
Explanation:
Step 1: To make Si equal on both sides. put 10 in front of HSiCl3
10 HSiCl3+ H2O →H10Si10O15+ HCl
Step 2: By putting 30 in front of HCl, Cl can be balanced
10 HSiCl3+ H2O →H10Si10O15+ 30 HCl
Step 3: Now, balance O by putting 15 in front of H2O
10 HSiCl3+ 15 H2O→H10Si10O15+ 30 HCl
Hence the balanced equation is:
10 HSiCl3+ 15 H2O→H10Si10O15+ 30 HCl
