Elements and atoms

Elements
Elements consist of only one kind of atom and cannot be decomposed into simpler substances.Elements consist of only one kind of atom and cannot be decomposed into simpler substances.
Our planet is made up of some 90 elements.Of these 90, only 25 or so are used to build living things.

Atoms
Each element is made up of one kind of atom. We can define an atom as the smallest part of an element that can enter into combination with other elements.

Each atom consists of
a small, dense, positively-charged nucleus surrounded by
much lighter, negatively-charged electrons.The nucleus of the simplest atom, the hydrogen atom (H), consists of
a single positively-charged proton. Because of its single proton, the atom of hydrogen is assigned an atomic number of 1.
a single electron.
The charge of the electron is the same magnitude as that of the proton, so the atom as a whole is electrically neutral. Its proton accounts for almost all the weight of the atom. The nucleus of the atom of the element helium (He) has
two protons (hence helium has an atomic number of 2) and
two neutrons. Neutrons have the same weight as protons but no electrical charge.
The helium atom has two electrons so that, once again, the atom as a whole is neutral.
The structure of each of the other kinds of atoms follows the same plan. From Lithium (At. No. = 3) to uranium (At. No. = 92), the atoms of each element can be listed in order of increasing atomic number. There are no gaps in the list. Each element has a unique atomic number and its atoms have one more proton and one more electron than the atoms of the element that precedes it in the list.