Understanding the Atom

1. Understanding the Atom 4-1: Basic Units of Matter

2. 4-1 Vocabulary • Matter • atom • nucleus • proton • neutron • electron • Democritus • Dalton • Lavoisier • Law of Conservation of Mass

3. What is the current atomic model? • Matter is anything that has mass and takes up space (such as solids, liquids and gases) • Sound, heat and light are not matter - they are forms of energy. • An atom is a small particle that makes up all matter. • Atoms are mostly empty space surrounding a massive central region of the atom called the nucleus.

4. What is the current atomic model? (cont’d) • Atoms contain three kinds of particles, two in the nucleus, and one outside the center of the atom. • Positively charged particles in the nucleus are protons. • Neutral particle in the nucleus is the neutron. • Negatively charged particles that move in the space outside an atom’s nucleus is the electrons.

5. What is the current atomic model? (cont’d) • An electron has about 1/2,000 the mass of a neutron or proton.

6. Interactive Atom

7. Is there historical evidence of atoms? • The Greek philosopher Democritus first (460 – 370 B.C.) coined the word atom, based on the Greek word atoma, meaning “indivisible” or “uncuttable”. • Democritus proposed that atoms were small, solid spheres. • The atom as Democritus described it was indivisible, meaning it was the smallest possible piece of matter that could not be cut into smaller pieces.

8. Is there historical evidence of atoms? (cont’d) • The French scientist Antoine Lavoisier conducted experiments that led to the Law of Conservation of Mass. It says that in any chemical reaction, the mass of the products of the reaction will always be equal to the mass of the materials at the beginning of the reaction.

9. Is there historical evidence of atoms? (cont’d) • The law of definite proportions, uncovered by French chemist J.L. Proust, states that pure compounds always contain the same elements in the same proportions by mass. • Water’s formula is H2O which means there are two Hydrogen atoms and one Oxygen atom in every molecule of water. • Water from your kitchen sink is the same as water from a glacier on Mars.

10. Is there historical evidence of atoms? (cont’d) • English schoolteacher and scientist John Dalton did many experiments on gases that led to a new and more complete model of the atom. • Dalton’s model had 5 major points.

11. Dalton’s Atomic Model • All matter is made up of atoms. • Atoms are neither created or destroyed in chemical reactions. (Law of Conservation of Mass) • Atoms of different elements combine in whole-number ratios. (Law of definite proportions) • Each element is made of a different type of atom. • The atoms of different elements have different masses and properties.

12. Dalton’s Atomic Model (cont’d) • Dalton used symbols to represent different elements, making it easier to write and communicate about the elements.

13. 4-1: Lesson Review Questions Which is NOT a particle in an atom? A positron B neutron C electron D proton

14. 4-1: Lesson Review Questions Which law states that the total mass of the starting materials equals the total mass of the product in a chemical reaction? A Dalton’s atomic model B the law of conservation of mass C the law of definite proportions D Democritus’ law

15. 4-1: Lesson Review Questions ____ make up the nucleus of an atom. A Protons and electrons B Neutrons and electrons C Protons and neutrons D Neutrons and photons

16. Homework • Answer the three multiple choice lesson review questions. • Write a “Step-Up-To-Writing” style paragraph answering the following question regarding your notes: “Why are symbols for concepts and objects, such as elements, atoms, and their electrons, important tools to help people communicate? ”