Itty-Bitty Atoms

1. Itty-Bitty Atoms What Chemistry Is All About

2. Structure of the Atom • All matter in the universe is made up of tiny particles. • Each particle is too small to see. • The most basic units of matter are called ATOMS. • Atoms cannot be broken down into smaller pieces of matter by any common methods of separation.

3. Atoms are the Building Blocks

4. Different Kinds of Atoms • Scientists have identified over 100 different kinds of naturally-occurring atoms • Each kind of atom has unique properties and is called an ELEMENT. • An atom of an element cannot be broken down and retain its properties.

5. Particle of Helium 1 atom of 1 element

6. Particles of oxygen 2 atoms of 1 element

7. Particles of Water: 3 atoms of 2 elements

8. Models of the Atom

9. Born about 460 BC in Abdera, Thrace, Greece Died about 370 BC Concluded matter could not be divided into smaller parts forever. Used the word “atomos” to describe the smallest piece of matter. Democritus

10. Englishman Taught at a Quaker school Poor, not articulate and not a skilled experimentalist Color blind John Dalton (1766-1844)

11. Dalton’s Model • Matter is made up of tiny, indivisible particles • Each element has its own unique properties • Tiny, solid spheres • Atoms of each element are exactly alike • Atoms of different elements have different masses • Atoms of different elements can join to form compounds.

12. Discovered electrons in 1897 Model sometimes called the plum pudding model. Thought the atom was positively charged material with electrons scattered through it. J. J. Thomson (1859-1940)

13. Thomson’s Model • Atoms contained smaller, subatomic particles • Particles were negatively charged—he named them electrons • He reasoned that atoms must contain enough positive charge to balance the negative charge • Model looked like a chocolate chip cookie

14. Birth: Nelson, New England Residence: Great Britain Ernest Rutherford (1871-1937)

15. Rutherford’s Model • Positive charged particles are protons • Protons have a greater mass than electrons • Protons concentrated in a small area at the center of the atom. He called this the nucleus. • The nucleus contains nearly all of the mass of the atom and the rest of the atom is nearly empty space.

16. Residence: Denmark Won Nobel Prize for Physics 1922 Niels Bohr (1885-1962)

17. Bohr’s Model • Niels Bohr modified Rutherford’s model in 1913. • Electrons keep moving around the nucleus in a region called energy levels arranged in shells or rings. • By absorbing or releasing a specific amount of energy, electrons move from one energy level to another.

18. Electron Cloud Model • Electrons dart within an energy level in an ever-changing path. • If the nucleus was a marble on the 50 yard line of a football field, the electron cloud would extend to the end zones.

19. Inside the Nucleus • An atomic force holds protons (positively charged particles) and neutrons (neutral particles) tightly together inside the nucleus. • The neutrons have no charge but have the same mass as protons.

20. Atomic Numbers • The atomic number tells the number of protons and the number of electrons. • There are an equal number of protons and electrons.

21. Isotopes • Atoms of the same element with different numbers of neutrons.

22. Mass Number and Atomic Mass • Almost every atom contains one or more neutrons in its nucleus. • The total number of neutrons and the total number of protons in an atom is called the mass number of an element • Mass numbers are usually written with the Element symbol followed by a hyphen and then the mass number