Ch. 5Ch. 5

5.1 Dalton’s Atomic Theory

1. All elements are composed of indivisible atoms (atoms are divisible)

2. Atoms of the same element are identical3. Atoms of different elements can mix

together in whole number ratios to form compounds

4. Chemical reactions occur when atoms are separated

5.2 Structure of the Atom

• Atom: Smallest particle of an element that retains the properties of that element.

5.2 Component Particles of ElementsSubatomic symbol charge massparticleElectron e- -1 1/1840Proton p+ +1 1Neutron n0 0 1

Nucleus: Protons + Neutrons

electrons

Discovery of Particles JJ Thomson Experiment

• Passed an electric current (electrons in motion) through gasses at low pressure

• Electrodes connected to high voltage electricity so that charges would separate on the two plates– Anode (+)– Cathode (-)

• Glowing beam traveled from cathode to anode

– Indicated that electrons are negatively charged!!!!!

Rutherford Gold Foil Experiment• Alpha particles (He atoms

that have lost 2 electrons)

• Scientists believed + and – were evenly spaced in the atoms

• Expected small deflection for majority of beam

• Actual Results: majority passed straight through!!!! And the parts that did deflect had a large deflection

• Indicated that the atom is largely empty space!!!!

5.3 Distinguishing between Atoms

• Atomic number = # protons in nucleus– Identifies an element

• Mass Number = # protons + # neutrons

Isotopes: Same number protons, but a different number of neutrons

Mass number 1 2 3

H H HAtomic 1 1 1Number

Hydrogen-1 Hydrogen-2 Hydrogen-3

Isotopes: Same number protons, but a different number of neutrons

Mass number 1 2 3

H H HAtomic 1 1 1Number

Hydrogen-1 Hydrogen-2 Hydrogen-3

Journal: What is the proton number, neutron number, and mass number of Oxygen-17 and Oxygen-18?

Isotopes: Same number protons, but a different number of neutrons

Mass number 1 2 3 H H HAtomic 1 1 1Number

Hydrogen-1 Hydrogen-2 Hydrogen-3

Journal: What is the proton number, neutron number, and mass number of Oxygen-17 and Oxygen-18?

Oxygen-17 p:8, n: 9, mass:17Oxygen-18 p:8, n:10, mass:18

Journal

• The naturally occurring isotope of Lithium is Lithium-7. – What is the mass number of Lithium-7? – What is the atomic number of Lithium-7? – How many protons does lithium-7 contain? – How many neutrons does Lithium-7 contain?

Journal

• The naturally occurring isotope of Lithium is Lithium-7. – What is the mass number of Lithium-7? 7– What is the atomic number of Lithium-7? 3– How many protons does lithium-7 contain? 3– How many neutrons does Lithium-7 contain? 4

Atomic Mass

• An average of the masses of the isotopes

% abundance mass + % abundance mass of Isotope A IsotopeA Isotope B Isotope B

Example: The natural abundance for boron isotopes is 19.9% 10B (10.013 amu) and 80.1% 11B (11.009 amu). Calculate the atomic weight of boron.

% abundance mass + % abundance mass of Isotope A IsotopeA Isotope B Isotope B

Example: The natural abundance for boron isotopes is 19.9% 10B (10.013 amu) and 80.1% 11B (11.009 amu). Calculate the atomic weight of boron.

(19.9%) (10.013) + (80.1%) (11.009) = 10.81

Journal

Calculate the weight of silicon using the following information:

92.23% 28Si (27.9769amu)4.67% 29Si (28.9765 amu)3.10 % 30Si (29.9738 amu)

Calculate the weight of silicon using the following information:

92.23% 28Si (27.9769amu)4.67% 29Si (28.9765 amu)3.10 % 30Si (29.9738 amu)

(92.23%) (27.9769) + (4.67%)(28.9765) + (3.10%) (29.9738) =

= 28.08

• Lab Activity: Observing Chemical Reactions1+2+3 + Black

• Next Time in class we will look at the Organization of the Periodic Table (Ch. 5.4)