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Difference b/w Atomic number and mass number

(atomic number and mass number and their uses)

Elements: chemicals consisting of a unique and unique atom, the atom is the smallest structural unit in the material, and consists of the nucleus and the outer perimeter, the nucleus is a small particle carrying a positive charge and constitutes 99.9% of the weight of the atom, and contains protons and neutrons, and elements exist naturally such as Oxygen, or man-made, such as bromine, are classified according to their location in the periodic table, into metals and non-metals and semi-metals, and the elements are distinguished by their atomic numbers, as there are three cases, solid, liquid and gaseous state.

Atomic number

Is the number of protons inside the nucleus of an atom, which distinguishes each element atom from the atom of the other element, which determines the type of element and its characteristics and chemical and physical characteristics, and the atomic number of elements starts from 1, the atomic number of the hydrogen atom, the highest atomic number is 92, which is the atomic number of the uranium atom, if any element of a proton is lost or added to a proton, is transformed into another element, such as a helium atom that contains two protons. If one of them is lost, it turns into a hydrogen atom, and vice versa.

The atomic number is the number of protons in the nucleus of the element atom. Since the atoms of different elements are electrically neutral, it means that the number of protons = number of electrons. So it can be said that:

Atomic number (Z) = Number of protons (P + ) = Number of electrons (e – )

The atomic number of the characteristics of atoms of one element, where all the atoms of the same element atomic number are different from the atomic number of atoms of other elements.

English scientist Henry Mosley is the first to designate the atomic numbers of a number of elements using X-rays (X-rays)

Mass number

Are the number of heavy particles in the nucleus, the total number of protons and the number of neutrons, and the mass number is written to the left of the element symbol from the top, and to calculate the number of protons and neutrons in the atom, you must use the periodic table, where the number is shown at each element, and increase the number of mass leads to Atoms are radioactive, unstable physical properties, and they fission in order to reach a stable state. (atomic number and mass number) When the mass is small, the atom is light, and it fuses to reach a stable state.

is the sum of the protons and the numbers of neutrons in the nucleus of an element’s atom

Mass number (A) = Number of protons (P + ) + Number of neutrons (no )

It was agreed to write the mass number to the left of the chemical symbol of the element and in the upper corner the atomic number is written to the left of the chemical symbol and in the lower corner of the symbol:


Use the atomic number and mass number

The atomic number and mass number are used to form a complete picture of the atom, in terms of qualities and properties, and how strong the nucleus holds atoms.

  • Example 1: A carbon atom, its atomic number is 6, the mass number is 12, what is the number of neutrons?
  • The solution: by subtracting the mass number from the atomic number, we can get the number of neutrons, ie the number of neutrons = 12–6 = 6.
  • Example2: The atomic number of lithium is 3, and its atomic mass is 7, how many protons, neutrons, and electrons in a lithium atom?
  • The atomic number = 3, so the number of protons = 3, the number of electrons = 3.
  • The mass number = 7, so the number of neutrons = mass number – atomic number = 7 – 3 = 4.

Atomic Mass Unit

Due to the small mass of the atom and thus the small numerical value of this mass in the case of using the unit of mass recognized (gram and derivatives) where agreed by the International Bureau of Measurements in 1961 As a carbon atom 12 C Are caliber Standard To measure the atomic weights of the elements and selected carbon atom and weight (12 AMU) Atomic mass unit For them, the atoms of the elements weigh a relative unit called the mass of the atom, which is symbolized (AMU) Alternative to the unit of Gram and its derivatives.

The unit of mass of an atom can be defined as part of 12 Of the mass of carbon isotope 12 To illustrate, let’s take the following example:
It is said that the weight of the helium atom Equal 4 amu What is this? Intended weight of helium atom is equal 4 x 1/12 From the weight of carbon isotope 12 it can be said that the weight of the helium atom is 1/3 Weight of carbon isotope 12.

The unit of mass of an atom is sometimes called the unit of mass (Unified Mass unit) It is marked with U Or sometimes called Dalton.

Other definitions

  • IsotopeIsotopes are different forms of atoms of the same element, similar in chemical properties and atomic numbers, but they differ in what is known as mass number due to the different number of neutrons in their nuclei.
  • The mass number is the sum of the number of protons and neutrons inside the nucleus of an atom, which is the mass of only one isotope.
  • Atomic number: The number of protons inside an atom’s nucleus. It is also equal to the number of electrons in a neutral atom.

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