What are atoms composed of? What is the significance of atomic number and mass number?

Atoms are composed of three main subatomic particles: protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge (they are neutral), and electrons have a negative charge.

The atomic number represents the number of protons in the nucleus of an atom. It is a fundamental property of an atom that determines its chemical behavior and its identity as an element. In a neutral atom, the atomic number also represents the number of electrons surrounding the nucleus.

The mass number, on the other hand, represents the total number of protons and neutrons in the nucleus of an atom. It helps to determine the mass of the atom. The mass number is typically denoted as a superscript to the left of an element's symbol.

To find the atomic number and mass number of an atom, you can refer to the periodic table of elements. The periodic table lists every known element in order of increasing atomic number. The atomic number is typically located above or below the element's symbol on the table.

To find the mass number, you need to know the number of protons and neutrons in the nucleus. The number of protons is equal to the atomic number. The mass number is the sum of the number of protons and neutrons. It can be calculated by subtracting the atomic number from the mass number, or by rounding the atomic mass of the element to the nearest whole number.

It's important to note that atoms can have different isotopes, which means they have the same number of protons but different numbers of neutrons. Isotopes have the same atomic number but different mass numbers.