A Simple Model of the Atom

A Simple Model of the Atom

Atoms

  • An atom is the smallest unit of a chemical element that retains the properties of that element.
  • Atoms are the building blocks of matter and everything in the universe is composed of atoms.
  • Atoms are neutral because they contain an equal number of positive and negative charges.

The Atomic Structure

  • Every atom consists of a dense central core called the nucleus, which is surrounded by tiny particles called electrons.
  • The nucleus contains protons, which are positively charged, and neutrons, which have no charge.
  • Electrons are negatively charged particles that move around the nucleus in electron shells or energy levels.

Atomic Number and Mass Number

  • The atomic number (also known as the proton number) of an atom is the number of protons contained in its nucleus.
  • The mass number (or nucleon number) is the total number of protons and neutrons in the nucleus of an atom.
  • Atomic number identifies the element and the number of electrons in a neutral atom equals the atomic number.

Isotopes

  • Isotopes are variants of the same element with the same number of protons but different numbers of neutrons.
  • Isotopes of an element have the same atomic number but different mass numbers.

Electronic Configuration

  • Electronic configuration describes the arrangement of electrons in energy levels or shells around the nucleus of an atom.
  • The first energy level/shell can hold up to 2 electrons, the second can hold 8, and the third can also hold 8.
  • To find the electronic configuration for any given element, the number of electrons equal to the atomic number will be distributed in these shells based on the capacity of each.

Ion Formation

  • An ion is a charged particle formed when an atom either loses or gains electrons.
  • When atoms lose electrons, they become positively charged ions (cations).
  • When atoms gain electrons, they become negatively charged ions (anions).

Relative Atomic Mass

  • The relative atomic mass (Ar) of an element is an average value that takes into account the abundances of the isotopes of the element.
  • It is usually a decimal number and is the mass shown on the periodic table.

The Periodic Table

  • The periodic table is a systematic way of arranging elements into periods (horizontal rows) and groups (vertical columns).
  • Elements in the same period have the same number of electron shells.
  • Elements in the same group have the same number of electrons in the outermost shell and generally exhibit similar chemical characteristics.