Atom Panjgrainkalanb Fdk

ATOM • Atoms are made of smaller particles, called electrons, protons, and neutrons. • An atom consists of a cloud of electrons surrounding a small, dense nucleus of protons and neutrons. • The diameter of a typical nucleus is only about 1 × 10-14 m (4 × 10-13 in), or about 1/100,000 of the diameter of the entire atom.

PROPERTIES OF ELECTRONS • DISCOVERED BY SIR J.J.THOMSON • Electrons are tiny, negatively charged particles. • Each electron carries a single fundamental unit of negative electric charge, or –1. • Electrons travel around the nucleus of an atom •

PROPERTIES OF PROTONS • Protons carry a positive charge of +1, exactly the opposite electric charge as electrons. • The number of protons in the nucleus determines the total quantity of positive charge in the atom. • In an electrically neutral atom, the number of the protons and the number of electrons are equal, so that the positive and negative charges balance out to zero.

PROPERTIES OF NEUTRONS • Neutrons are about the same size as protons but their mass is slightly greater.

PROPERTIES OF ATOMS

• Atoms have several properties determining how they change under certain conditions.

ATOMIC NUMBER • Atomic number is the number of protons in an atom. As the atoms are normally electrically neutral, the atomic number also specifies how many electrons an atom will have. • It is shown by the alphabet ‘Z’. • The lightest atom, hydrogen, has an atomic number equal to one, contains one proton, and (if electrically neutral) one electron.

MASS NUMBER • Mass number is the total number of neutrons and protons in an atom. • It is represented by the English alphabet ‘A’. • The mass number of an atom is approximately the mass of an atom

ATOMIC MASS AND WEIGHT • Atomic mass of an atom is measured in terms of unit called atomic mass unit (amu). • amu is defined as 1/12th of the mass of carbon atom. • Atomic mass of an atom (protons + neutrons) also relates to the atomic weight of an element in grams.