Ch. 3-1 The Atom Atomic Structure

POINT > Explain the law of Conservation of Mass POINT > Explain the law of Definite Proportions POINT > Explain the law of Multiple Proportions POINT > Describe five points of Dalton’s atomic theory

Democritus (460 – 370 BC) First to suggest existence of atoms Believed atoms were indivisible and indestructible, but (obviously) lacked scientific evidence

1780s: Chemists (like Lavoisier) started accurately measuring masses Ancient Greeks: Can matter be divided into ever-smaller pieces, forever? Aristotle: yes Democritus: no 1780s: Chemists (like Lavoisier) started accurately measuring masses No evidence either way for 2000 years

POINT > Explain the law of Conservation of Mass Careful measurements led to discovery of key principles: The mass of reactants before a reaction and the mass of products after a reaction are always the same… Conservation of Mass: mass is not created or destroyed during chemical reactions

POINT > Explain the law of Definite Proportions Careful measurements led to discovery of key principles: Law of Definite Proportions: A given compound always contains the same elements in exactly the same proportions

Water is always 11.1% hydrogen and 88.9% oxygen. This demonstrates WB CHECK: Water is always 11.1% hydrogen and 88.9% oxygen. This demonstrates a) that oxygen is 8 times heavier than hydrogen b) the law of Definite Proportions c) the law of Conservation of Mass What is the law of Conservation of Mass?

POINT > Explain the law of Multiple Proportions Elements always combine in whole number ratios Law of Multiple Proportions: Elements combine in small whole number ratios to form compounds (ex. H2O and H2O2)

A) C6H12O6 and CH4 B) PCl3 and PBr3 C) SO2 and SO3 D) H3PO4 and PO4- WB CHECK: Which combination of compounds could be used to demonstrate the law of Multiple Proportions? A) C6H12O6 and CH4 B) PCl3 and PBr3 C) SO2 and SO3 D) H3PO4 and PO4-

POINT > Describe five points of Dalton’s atomic theory John Dalton (1766 – 1844) Put Democritus’ ideas on atoms and the Laws we’ve discussed into a scientific theory

POINT > Describe five points of Dalton’s atomic theory All elements are composed of atoms

POINT > Describe five points of Dalton’s atomic theory Atoms of the same element are identical; atoms of one element are different from those of another element

POINT > Describe five points of Dalton’s atomic theory. Atoms of different elements can physically mix together or chemically combine to form compounds

POINT > Describe five points of Dalton’s atomic theory. Chemical reactions occur when atoms are separated, joined, or rearranged

POINT > Describe five points of Dalton’s atomic theory 5. Atoms cannot be created, destroyed or sub-divided

POINT > Describe five points of Dalton’s atomic theory. Dalton’s Theory still stands, with modifications: 1. All atoms of an element are not identical (isotopes) 2. Atoms can be sub-divided (into protons, neutrons and electrons)

WB CHECK: Which part of Dalton’s Theory describes the Law of Multiple Proportions? A) All matter is made of atoms B) Atoms cannot be subdivided, created, or destroyed C) Atoms of different elements combine in simple whole-number ratios to form chemical compounds D) In chemical reactions, atoms are combined, separated, or rearranged

WB CHECK: Which of these parts of Dalton’s atomic theory is no longer accepted? A) All matter is made of atoms B) Atoms cannot be subdivided, created, or destroyed C) Atoms of different elements combine in simple whole-number ratios to form chemical compounds D) In chemical reactions, atoms are combined, separated, or rearranged

Atomic Size Most atoms have a radius ranging from 5 x 10-11 m to 2 x 10-10 m A penny-sized amount of pure copper has 2.4 x 1022 atoms (To contrast, human population just passed 7 x 109)

Homework: Read pages 63-67 F.A. #1-3 page 67 Read ahead in Ch. 3