Science CUP

Give reasons The number of electrons of an ion differs from that of its atom.

• Because the number of electrons in ion is less than or more than its number in the same atom by the number of lost or gained electrons.

• Because it arises by sharing each nitrogen atom with three electrons to complete its outermost shell with 8 electrons and becomes more stable

• Because sodium ion is formed when sodium atom loses one electron and changes

• while covalent bond arises between two similar or different nonmetal

The number of known elements up till now is elements.

• 92

• 118

• 121

• 181

When an atom is changed into an ion, the..............

is changed.

• number of protons

• number of neutrons

• number of electrons

• mass number

A lithium atom (Li) changes into a lithium ion (Li +), which mean that it................

• gains one proton.

• gains one electron.

• loses one proton.

• loses one electron

The only nonmetal that exists in a liquid state is.....................

• bromine,

• chlorine.

• hydrogen.

• nitrogen.

The number of electrons in oxygen ion (0-2) is......................... electrons.

• 6

• 8

• 10

• 12

The number of......................... determines the type of element and its chemical activity.

• electrons in the outermost energy level

• levels filled with electrons

• neutrons

• protons

All the following are properties of inert gases except....................

• they don't participate in chemical reactions.

• their outermost electron shells are completely filled.

• they form negative ions.

• their molecules consist of one single atom.

During the formation of a sodium chloride molecule, sodium atom..........................

• gains one electron from chlorine atom,

• gives one electron to chlorine atom.

• gains two electrons from chlorine atom.

• gives two electrons to chlorine atom.

The bond in a sodium chloride molecule is ...........................bond.

• single covalent

• double covalent

• triple covalent

• ionic