Atomic Structure: Atoms and Their Components

Elements, Compounds, and Molecules

• Elements are the simplest pure substances that cannot be simplified to give new substances.
• There are more than 90 naturally occurring elements in nature.
• Examples of elements include sodium (Na), hydrogen (H), oxygen (O), iron (Fe), gold (Au), and uranium (U).

Compounds

• A compound is a pure substance made up of atoms of different elements chemically combined.
• Examples of compounds include sodium chloride (NaCl), carbon dioxide (CO2), glucose (C6H12O6), and sulfuric acid (H2SO4).

Molecules

• A molecule is formed when two or more atoms bond together.
• Examples of molecules include molecular hydrogen (H2), molecular oxygen (O2), and molecular nitrogen (N2).
• Water (H2O), carbon dioxide (CO2), methane (CH4), and sodium chloride (NaCl) are compound molecules because each is made from more than one type of element.
• All compounds are molecules, but not all molecules are compounds.

Charge of the Atom

• The nucleus includes Z protons of electric charge +e each, making its total electric charge +Ze.
• The electron cloud includes Z electrons of electric charge -e each, making its total electric charge -Ze.
• The total electric charge of the atom is equal to zero because the number of protons is equal to the number of electrons.

Subatomic Particles

• Proton: +1 relative charge
• Neutron: 0 relative charge
• Electron: -1 relative charge

Mass of the Atom

• The mass of an electron is negligible compared to the mass of a nucleon (proton or neutron).
• The mass of the atom is equal to the mass of its nucleus.

Isotopes

• Isotopes are different versions of an element with the same number of protons but a different number of neutrons.
• Examples include hydrogen atoms with no neutrons, one neutron, or two neutrons.

Ions

• Ions are electrically charged atoms formed when atoms gain or lose electrons.
• The loss or gain of electrons never modifies the number of protons in the nucleus.
• Ions can be either positively charged or negatively charged.
• Polyatomic ions are formed when several atoms combine.

Atomic Structure

• Atoms are composed of protons, electrons, and neutrons.
• Protons carry a positive electrical charge, electrons carry a negative electrical charge, and neutrons carry no electrical charge.
• The nucleus is the central part of the atom containing protons and neutrons.
• Electrons are arranged around the nucleus in electron clouds or electron shells.

Nuclide and Atomic Number

• The number of protons in the nucleus of an atom is the atomic number of that atom, represented by the letter Z.
• X represents the chemical symbol of an element, where A is the mass number and Z is the atomic number.
• If n is assigned to the number of neutrons found in a nucleus, then A = Z + n.

Learn about the basic building blocks of matter, including the composition of atoms and the properties of protons, electrons, and neutrons.