Chromium – Cr

20Ca

Atoms which have the same atomic number but different mass numbers are isotopes. For example, all calcium atoms have an atomic number of 20 but there are three isotopes of calcium – 39, 40, and 42….Structure of an Atom.

C) Correct. Because the mass number of an atom is the sum of proton number and neutron number of the atom. So, 18 + 20 = 38.

Ca2+

#18 – Argon – Ar.

Chlorine-35

Sulfur – S

Explanation: You gots Z=18 , the atomic number, where Z is the number of nuclear protons. The number of protons defines the element….and thus we got calcium…. ….and with 20 neutrons we got the 38Ca isotope….the which is rather short-lived….

potassium

Argon

Ar

Hydrogen

18

2,8,8

Argon prevents the oxidation of the surface as the plasma breaks the oxygen bond with the metal surface and carries it out of the chamber. Argon is also used after CF4 (or a CF4/O2 mixture) is used to etch a product (remove material).

Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in the Earth’s atmosphere, at 0.934% (9340 ppmv).

(6) For molecules Mr is the relative molecular mass or molecular weight; for atoms Mr is the relative atomic mass or atomic weight and the symbol Ar may be used.

Follow these steps to calculate accounts receivable:

1. Add up all charges. You’ll want to add up all the amounts that customers owe the company for products and services that the company has already delivered to the customer.
2. Find the average.
3. Calculate net credit sales.
4. Divide net credit sales by average accounts receivable.

The A r values for elements are often stated in the periodic table. The relative atomic masses of elements are proportional measures. For example, the A r for carbon is 12, and the A r for magnesium is 24. This means that magnesium atoms are twice the mass of carbon atoms.

1

Fact box

The relative formula mass of a substance made up of molecules is the sum of the relative atomic masses of the atoms in the numbers shown in the formula . Relative formula mass has the symbol, M r.

Molar mass of H = 1.00794 g/mol.

The formula mass of a molecule (also known as formula weight) is the sum of the atomic weights of the atoms in the empirical formula of the compound. Formula weight is given in atomic mass units (amu).

Avogadro’s number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance. It is equal to 6.022×1023 mol-1 and is expressed as the symbol NA. Avogadro’s number is 6.022×1023 molecules.

Avogadro’s number, number of units in one mole of any substance (defined as its molecular weight in grams), equal to 6.02214076 × 1023. The units may be electrons, atoms, ions, or molecules, depending on the nature of the substance and the character of the reaction (if any).

The term “Avogadro’s number” was first used by French physicist Jean Baptiste Perrin. If you divide the charge on a mole of electrons by the charge on a single electron you obtain a value of Avogadro’s number of 6.02214154 x 1023 particles per mole.