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Holt McDougal Chapter 4 Section 2. Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms.

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Presentation on theme: "Holt McDougal Chapter 4 Section 2. Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms."— Presentation transcript:

1 Holt McDougal Chapter 4 Section 2

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3 Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their mass, electrical charges and locations within the atom

4 What scientists helped to develop atomic theory? What part of atoms did Thomson discover? What part of atoms did Rutherford discover?

5 Democritus Greek philosopher in 4 th century BCE Tiny, indivisible units and void Atomos unable to be cut or divided No evidence; all conjecture and theory

6 1808, British schoolteacher John Dalton performed experiments Atoms DO exist! Atoms could form compounds Law of Definite Proportions

7 How was Daltons theory different from that of Democritus? Carbon makes up 27% of the mass of CO2. How many grams of C are there in 88g of CO2?

8 1897, British scientist J.J. Thomson working with cathode rays Discovered electrons, negatively charged particles Plum Pudding by another Thomson called Lord Calvin

9 What was the Greek perspective of atoms? How did Dalton support and detract from the Greek perspective of atoms? How did JJ Thomson discover electrons?

10 Was a student of Thomson Tested the idea that the mass of an atom was spread evenly over its volume Gold Foil experiment Bounce back indicates a concentrated center

11 Rutherford concluded that atoms positive charge is concentrated at the center Nucleus dense positively charged core of atom So tiny that like a marble in a football stadium Negative electrons orbit the nucleus

12 No specific orbits Only established the existence of the positive nucleus

13 ScientistContribution First proposed that the universe is made up of tiny, indivisible units called atoms Carried out scientific experiments that showed that atoms exist Showed that atoms contain smaller particles called electrons Showed that the positive charge in an atom is concentrated in a nucleus at its center

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15 Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their ass, electrical charges and locations within the atom

16 What do atoms of the same element have in common? What are isotopes? How is an elements average atomic mass calculated?

17 ScientistContribution First proposed that the universe is made up of tiny, indivisible units called atoms Carried out scientific experiments that showed that atoms exist Showed that atoms contain smaller particles called electrons Showed that the positive charge in an atom is concentrated in a nucleus at its center Democritus Dalton Thomson Rutherford

18 1913, Danish physicist Neils Bohr Fixed orbits for the electrons James Chadwick, Bohrs student Found the neutron in the nucleus Led to discovery of fission and the atomic bomb

19 Established by 1926 Area where electrons are most likely to be found 100,000 times larger than the diameter of the nucleus Impossible to accurately describe path and location at any given time Orbital a region in which an electron is most likely to be

20 ParticleChargeMass (kg)Location Proton+11.67 x 10 -27 Inside the nucleus Neutron01.67 x 10 -27 Inside the nucleus Electron9.11 x 10 -31 Outside the nucleus

21 The number of protons is the same!!! # of protons identify the atom and element

22 Protons positive Electrons negative 1 proton + 1 electron = neutral charge Gain/lose electron = ion (ionized atom) Ions are NOT neutral

23 Opposites attract Protons and electrons attract each other Farther apart = less attraction

24 Atoms of same element = same # protons Atomic # = # of protons Neutral atoms means the atomic # = protons = electrons (i.e., net charge = zero)

25 Find the atomic number and name for the following elements: 1. H 2. Sc 3. Ta 4. Bh 5. F 6. Sn 7. U Hydrogen 1 Scandium 21 Tatalum 73 Bohrium 107 Flourine 9 Tin 50 Uranium 92 How many electrons does each of the listed elements have?

26 Most atoms have protons and neutrons Atomic Mass # = protons + neutrons Atomic Mass = Atomic Number + neutrons How can atoms of the same element have different mass #s when they all MUST have the same atomic #?

27 Which two types of subatomic particles are located in the nucleus? How does the mass of an electron compare with the mass of a proton? Why are atoms neutral? What force holds atoms together?

28 Atoms of an element with different mass #s Remember, the AN (# of protons) is ALWAYS the same # of neutrons is different from one isotope to another

29 Protium Deuterium Tritium What is the atomic number, atomic mass, and electrical charge for each?

30 Some more than others (e.g., O has AM of 16 usually; about 0.2% have mass of 18) Some isotopes are unstable and decay How can decayed isotopes form new/different isotopes of the same element (even though they are breaking apart)?

31 35 17 Cl Chemical symbol represents the element AMN is written on top AN is written on bottom How can you compute the number of neutrons?

32 Too tiny 1 atom of F has mass (kg) of less than one trillionth of one billionth of one gram 111 1,000,000,000,000,000X1,000,000,000,000X1 What do you think that number looks like? Write it down and compare with your neighbor

33 Describes the masses of atoms SI standard of measure for atoms A AMU = 1/12 mass of C-12 atom Mass number = protons + neutrons (i.e., whole number) Atomic mass = mass of single atom of element (i.e., usually a decimal)

34 What is the AN of most atoms of O? What is the AMN of most atoms of O? How many protons are in the nucleus of an atom of Cl? What unit do scientist use to measure the masses of atoms?

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