Which electron configuration represents anatom of magnesium in an excited state?
(1) 2–7–3 (3) 2–8–2
(2) 2–7–6 (4) 2–8–5

The answers are (1) and (3). Because the number of atoms in magnesium is 12.

Further Explanation

The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus. The amount is identical to the amount of charge in the core. The atomic number uniquely identifies chemical elements. In uncharged atoms, the atomic number is also the same as the number of electrons. The sum of atomic numbers Z and the number of neutrons N gives the mass number A of an atom. Because protons and neutrons have roughly the same mass (and the mass of electrons is ignored for many purposes) and nucleon bond energy is always small compared to nucleon mass, when the atomic mass of each atom is expressed in units of integrated atomic mass (into a quantity called "mass relative isotope "), worth about 1% of all A. numbers. Atoms with the same atomic number Z but neutron N numbers are different, and therefore have different atomic masses, known as isotopes. More than three-quarters of the elements present in nature are in a mixture of isotope conditions, and the average mass of the isotope for the mixture of isotopes of an element (called relative atomic mass) in the environment on Earth, determines the standard atomic weight of the element. Historically, the weight of these atomic elements (compared to hydrogen) is the amount that can be measured by chemists in the 19th century.

The writing of the elemental symbol was introduced in the Middle Ages by John Dalton (1810) who made a very simple elemental symbol as a circle. Along with the development of the discovery of the element J.J Berzelius (1779-1848) made the symbol of the element that is used as the basis for writing the element symbol until now, with the provisions: one symbol element consisting of one letter, then the writing must be in capital letters. Two symbol elements consisting of two letters, then the writing with capital letters in the first letter, and lowercase letters for the second.

The chemical formula of a substance states the type and the relative number of atoms contained in that substance. The number that states the number of atoms of an element in a chemical formula is called the index number. Chemical formulas may be either molecular formulas or empirical formulas.  

The formula could be a formula that states the number of atoms of the weather that frame one molecule of a compound. So the molecular formula expresses the actual arrangement of matter molecules.

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Grade: High School

Subject: Chemistry

keywords: The atomic number