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The Atom

Explore the world of atoms, elements, compounds, and chemical bonding in this beginner-friendly guide. Learn about the structure of atoms, the periodic table, compounds, and more. Discover how atoms combine to form compounds and the role of ions in chemical reactions.

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The Atom

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  1. The Atom • Matter is anything that has mass and takes up space • Living and nonliving things are made up of tiny units called atoms. • The center core is called the nucleus. • Chemistry really involves • electrons

  2. The Atom • The nucleus is made up of particles called protons and neutrons • Protons have a positive charge (+1) and neutronshave no electrical charge (0). • Negatively charged particles, called electrons (-1) revolve around the nucleus at different distances from the nucleus.

  3. The Atom • The electrons move in paths called shells or energy levels. • Atoms have the same number of electrons and protons. Therefore, they are electrically neutral (have no electrical charge).

  4. Elements • There are about 100 different kinds of atoms known to scientists today. • A substance made up entirely of one kind of atom is called an element. • Ninety-two elements occur naturally and the others were made up in a laboratory. • Elements differ from one another in their proton, neutron, and electron number.

  5. The Periodic Table of Elements

  6. Most Common Elements

  7. Elements • An element cannot be broken down into any other substance or matter. • Pure silver is an element. • It is made up only of silver atoms. • When you break down a silver atom, you get electrons, protons, and neutrons.

  8. Element Symbols • Each element is represented by a symbol made up of one or two letters.

  9. Compounds • A compound is formed when two or more elements combine chemically.

  10. Compound Properties • The properties (characteristics) of compounds are quite different from the properties of the elements of which they are composed. • For example, table sugar is made up of the elements carbon, hydrogen, and oxygen. • Carbon is a black solid, and hydrogen and oxygen are colorless gases. • However, when they combine chemically they form a white granular substance.

  11. Compounds • Elements combine to form compounds by a process called chemical bonding. • The formation of a chemical bond involves either the transfer of electrons from one atom to another, or the sharing of electrons between atoms.

  12. Chemical Bonding

  13. Molecules • A molecule of a particular compound is made up of definite numbers and kinds of atoms bonded (joined) together. • A molecule of water contains two hydrogen atoms and one oxygen atom bonded together. • Two atoms of hydrogen bond together form a molecule of hydrogen.

  14. Ions • An ion is an atom that has gained or lost an electron. • Ions are formed during chemical bonding that involves the transfer of electrons. • When electrons are transferred from one atom to another, both atoms become electrically charged. • The atom that loses electrons becomes positively charged. • The atom that gains electrons becomes negatively charged. • The ions with opposite electrical charges are attracted to one another.

  15. Ionic Bonds • A chemical bond formed when atoms lose or gain electrons is called an ionic bond.

  16. Covalent Bonds • Covalent bonds are formed when atoms produce compounds by sharing electrons. • When making hydrogen gas, one molecule of hydrogen gas is formed when two hydrogen atoms join by sharing electrons.

  17. . Chemical Formulas • A chemical formula represents the chemical makeup of a compound. • It shows the numbers and kinds of atoms present in a compound. • It is a kind of “shorthand” that scientists use.

  18. Formula Examples • The chemical formula for sugar is C6H12O6 • This means that in one molecule of sugar there are six carbon atoms, twelve hydrogen atoms and six oxygen atoms. • H2O (water) • SO2 (sulfur dioxide) • CO2 (carbon dioxide)

  19. Structural Formulas • A formula can also show the kinds, numbers, and arrangement of atoms. • This is called a structural formula. • Here is the structural formula of Hydrogen.

  20. Equations • Equations are used to describe chemical reactions. • The substances that start the reaction are called the reactants. • The reactants are placed on the left side of the equation. • The substances formed by the reaction are called the products. • The products are placed on the right side of the equation. • The arrow means “to make” or “to form”.

  21. Equations • Reactions may be represented either by words or formulas. • The word equation for aerobic respiration is: (enzymes) SUGAR + OXYGEN  ENERGY + CARBON DIOXIDE + WATER • An equation using formulas instead of words is called a chemical equation. • The chemical equation for aerobic respiration is: C6H12O6 + O2 6H2O + 6CO2

  22. Organic and Inorganic Compounds • Living things are made up of inorganic and organic compounds. • Compounds that do not contain both carbon and hydrogen are called inorganic compounds. • The principal inorganic compounds found in living things are: • water • salts • inorganic acids • Inorganic bases

  23. Organic and Inorganic Compounds • Organic compounds are compounds that contain both carbon and hydrogen. • The classes of organic compounds found in living things are: • Carbohydrates • Proteins • Lipids • Nucleic acids

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