Atoms+and+Isotopes


 * What is an Atom?**

The **atom** is a basic unit of [|matter] that consists of a dense, central [|nucleus] surrounded by a [|cloud] of [|negatively charged] [|electrons]. The [|atomic nucleus] contains a mix of positively charged [|protons] and electrically neutral [|neutrons]



What are Isotopes? Give Examples
Atoms with the same number of protons belong to the same element. Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei. P=E=N Protons =Electrons= Number

For example, all lithium atoms have three protons,three elctrons and its atomic number is three.

Ninety-three per cent of all lithium atoms have three neutrons. The rest have four. Hence lithium has two isotopes, which we can write as:

Uranium atoms always have 92 protons. The most common isotope has 146 neutrons, a less common isotope has 143 neutrons and a few have 142 neutrons. Mass number - atomic number = Neutrons Hence we can write them as:

An element whose atoms emit nuclear radiation is said to be radioactive. Uranium and most of the elements after it in the periodic table (atoms of higher atomic number) are radioactive. Not surprisingly, a radioactive isotope is called a radioisotope. Structure of the Atom

All matter is made up of atoms. An atom is like a tiny solar system. In the center of the atom is the nucleus which is a cluster of protons and neutrons. The **protons** have a **positive** electric charge while the **neutrons** are electrically **neutral**. The nucleus makes up almost all of an atom's mass or weight. Whirling at fantastic speeds around the nucleus are smaller and lighter particles called **electrons** which have a **negative** electric charge.

An atom has the same number of electrons (- ve charge) and protons (+ ve charge) to make the atom electrically neutral. An extremely powerful force, called the nuclear force, holds the protons together in the nucleus as they naturally repelled one another electrically.

The atoms of each [|**chemical element**] have a different nucleus. An atom of hydrogen has one proton and no neutrons. An atom of nitrogen has 7 protons and 7 neutrons. Heavy elements have a large number of protons and neutrons. For example, the most common [|**isotope**] of uranium, uranium-238 has 92 protons and 146 neutrons in its nucleus.

The drawing on the left shows a **carbon** atom with 6 protons, 6 neutrons and 6 electrons.

Atoms are the building blocks for all matter. Everything except energy in the universe is made up of matter. Atoms are composed of three subatomic particles, protons, neutrons and electrons. Recall: Neutrons- neutral Protons- positive charge Electrons- negative charge Proton's and Neutrons are found in the nucleus and electrons are found in the outer shells. The first shell can only hold 2 electrons and the ones after that can hold 8.