What Is An Atom?

  atoms all matter is made of elements

substances that cannot be broken down by

chemical activity an atom is the

smallest particle of an element that

retains the elements properties atoms

are the building blocks for everything

in the universe including ourselves

people often think of atoms as the

smallest possible forms of matter but

even smaller particles make up atoms

each atom has a dense Center called a

nucleus the nucleus contains neutrons

which have a neutral electric charge and

protons which are positively charged the

number of protons in an atom determines

an elements physical properties no two

elements have the same number of protons

revolving around the nucleus like

planets around the Sun are negatively

charged particles called electrons

electrons and protons attract each other

so atoms usually have equal numbers of

the two particles scientists assign

atoms and atomic number and atomic mass

unit the atomic number is the number of

protons present in the atom for instance

a helium atom has two protons so

helium's atomic number is to add the

number of protons and neutrons in an

atom's nucleus together and you get the

atomic mass unit or amu a helium atom

has two protons and two neutrons so has

a mass of four AMU electrons have almost

no mass and are not included in AMU

calculations on atoms number of protons

remains constant individual atoms can

lose or gain electrons atoms with

different ratios of electrons two

protons are called ions atoms of the

same element can also have extra

neutrons scientists call atoms with

extra neutrons isotopes despite having

different Neutron counts isotopes retain

their elements chemical properties

because the number of protons remains

constant.