To cut this short and for your understanding, ionic bond is formed between metals (mostly right column in periodic table). Covalent bond is formed between non-metals (mostly left column in periodic table). So polar covalent is also a covalent bond but it is polar, which means the shape of molecules are not symmetrical hence maybe an atom in a molecule has most of the electron attracted to it causing itself to be partial negative (since electron are negatively charged) and the other atom has its electron being attracted by others became partial positive. Polar covalent can also be when H atom is binding either to F, O or N (also known as hydrogen bond).
It has to be a metal, it can't be anything else.
There are several scales to determine the weight of material. The chose of the weight scale depends upon the size of the material. Like if we have to measure the molecular or atomic weight of a molecule or atom we use gm. Like that for the bigger molecules like proteins the weight of the molecule is expressed by different scale due to its big size. Like that for big material like iron rods etc we generally use kilograms or ton. There are two types of measuring units one is C.G.S. and another is S.I. The S.I. units are more acceptable worldwide than that the C.G.S. units as the digit comes in SI units are easily handable than that of CGS.
Thus metric is used to determine a large weight of compounds which is a SI unit and handable.
Answer:
Periods on the periodic table of elements
Explanation:
In the periodic table of elements, there are seven horizontal rows of elements called periods. The vertical columns of elements are called groups, or families. (See also The Periodic Table: Metals, Nonmetals, and Metalloids.) In each period (horizontal row), the atomic numbers increase from left to right.
