Name ____________________________ Hr ______

Unit 5: The Atom NotesEarly Ideas About MatterDermocritis Matter is composed of atoms- coined the word atom

Different kinds of atoms have different sizes, shapes and masses these determine the properties of the matter

Dalton All matter is composed of atoms

Atoms are indivisible andIndestructible

All atoms of the same element are identical

Atoms of one element are differentfrom those of another element.

o Elements can be identified andDistinguished from each other.

Atoms combine to form _compounds in simple ___whole – number ____ ratios.

o EX: XY, X2Y, XY2 NOT X3/4Y or X2.3Y

In a chemical reaction, atoms arerearranged

o Law of Conservation of Mass

JJ Thomson Discovered electrons with his cathode ray

____________ experiment.

He calculated the charge to mass ratio of the particle and

found that the mass of an electron is less than

___________ the mass of the lighest known element (H).

•JJ Thomson identified the first ___subatomic particle_ - the

electron!!!

Thomson’s Plum Pudding ModelElectrons are negative but matter is __neutral_...

There must be some _positive_ charge.

Thomson proposed atoms were uniformly positive spheres with electrons _scattered evenly throughout

Rutherford

Atom is made up of mostly empty space

Atom has a small dense positive center in the center

Gold Foil Experiment

Rutherford’s Model of the Atom

Niels Bohr Observed that when energy was added to a sample of

hydrogen gas a distinct color was given off

Atoms contained fixed energy levels which kept electrons from falling into the nucleus

Electrons orbit around the nucleus in certain paths(energy levels)

Bohr’s Model of the Atom

Final Development of the atomic theory Schrodinger- electron cloud model. Found probabilities

of where electrons can be found

Heisenburg – cannot know both the position and momentum of an electron. The more you know about one of these the less you know about the other

Chadwick- discovered the neutron. Neutron is located in the nucleus and has no charge but the same mass as a proton

Defining the Atom

Atoms are…the smallest particle of an element that retains the properties of the element

Modern Model of the Atom An atom is mostly empty space Small, dense nuclues which contains _protons and neutrons. Electrons _, which carry one negative charge_, are located in the space surrounding

the nucleus. Draw an atom →

Particle Symbol Relative Charge

Relative Mass

Actual Mass (g)

Electron e- 1- 1/1840 9.11 x 10-28

Proton P+ 1+ 1 1.673 x 10-24

Neutron n 0 1 1.675 x 10-24

Telling Atoms Apart Atomic number: # of protons

Idenfitying characteristic of an elementIn neutral atoms, #protons = # electrons

Ions are…atoms with a positive or negative charge

o If an atom gains electrons it becomes negativeF- a flourine atom gained 1 electron

o If an atom loses electrons it becomes positiveCa2+ a calcium atom lost 2 electrons

Calculating the charge: Charge = # protons - # electrons only the number do not include the charge!

Element Atomic Number Protons Electrons

Pb 82 125 82

Zn 30 35 30

O2- 8 8 10

Na+ 11 12 11

Mass number: total number of protons and neutrons

How do we figure out how many neutrons?Atomic number

Isotopes Isotopes: atoms with the same number of protons and different number of neutrons

o Ex: Potassium always has 19 p+ & 19 e- but it can have 20, 21, or 22 neutrons.Because isotopes have a different number of neutrons, they have different mass numbers .Isotopes of the same element have the same chemical properties because they have an identical number of protons and electrons.

Isotope Symbol Protons Electrons Neutrons

Carbon-12 C 6 6 6

Carbon-13 C 6 6 7

Carbon-14 C 6 6 8

Atomic Mass Most atoms in nature are found as a mixture of _____isotopes

o For example 69.2% of the copper atoms found on Earth are the copper-63 isotope and the other 30.8% are copper-65.

The average atomic mass on the periodic table is the average mass of all the isotopes that exist for a certain element multiplied by their percent abundance

Atomic Theory Worksheet - Historical Development of the modern model of the atom.

12C6

1. Draw below the model of the atom proposed be the following individuals:Dalton (1800) Thompson (1897) Bohr (1913)

2. How did Thompson’s model differ from Dalton’s model?

3. The gold foil experiment resulted in two major discoveries which were made about the structure of the atom. What were they?

1.

2.

4. How does the Bohr model represent electrons around the central nucleus? Why?

5. The modern model of the atom is called the wave mechanical model. In the wave mechanical model electrons are located around the nucleus based on the probability of finding an electron in a certain area. These areas are called:

a. shells b. orbitals c. rings d. waves

6. Match the correct statements with the word in the box. Put the number that corresponds to the statement in each box.

Democritus_____

Dalton_____

Thompson_____

Electron cloud______

Rutherford_____

Proton_____

Atom_____

Bohr_____

Wave Model_____

Neutron_____

Nucleus_____

Alpha particle_____

Electron_____

Model______

Energy levels_____

Mass number_____

                                                                                                                1. Made a mental model of the atom; Greek philosopher2. Used by Rutherford in his experiment; made of two protons and two neutrons3. The paths in which electrons circle the nucleus according to the Bohr model4. The positive particle in the nucleus of an atom5. The tiny positive core of an atom; contains protons and neutrons6. Formed the Atomic Theory Model of the atom; English schoolteacher7. Discovered the nucleus using his gold foil experiment8. Current explanation of where electrons might be found in the atom9. Used by scientists to explain something we cannot see or understand10. The smallest particle of an element that has the properties of that element11. Current model of the atom; proposed by Schrodinger12. Mass of protons and neutrons13. Developed the model of the atom in which electrons orbit the nucleus in

energy levels14. The negative particle that circles the nucleus15. The neutral particle in the nucleus of an atom16. Proposed the “plum-pudding” model of the atom; discovered the electron

Name ________________________________Date ________________________ Hr ______

1. An atom has a mass number of 32 and it also has 16 electrons.a. How many protons does this atom have? ________b. What is the identity of this atom? ________c. How many neutrons does this atom have? ________

2. A certain ion has an atomic number of 13, a mass number of 27, and 10 electrons.a. What is the charge on the ion? ________b. What is the identity of the ion? ________________c. How many neutrons does the nucleus of this ion have? ________

3. What is the charge on a magnesium ion that has 10 electrons? ________

4. Identify the element with 38 protons and 45 neutrons ________________________.

5. What must be done to a neutral chlorine atom in order to change it into Cl- ?

6. How does Ca differ from Ca2+?

7. Complete the following table:

ChemicalSymbol

# of protons

# of neutrons

# of electrons Atomic # Mass #

136 Ba2+

56

26 26 56

120 79 79

19 20 18

Average Atomic Mass Practice

Analyzing a Spectrograph

A mass spectrometer is an instrument used to separate an element's isotopes and to measure their relative abundances. Within this device, a sample of an element is vaporized, then ionized and accelerated down a tube. Near the end, the beam of ions is passed through a strong magnetic field which exerts a force on the ions. Ions of greater mass possess more inertia, or more of a tendency to continue to move in a straight line, and so deviate only slightly from their projected path. Ions of lesser mass are more greatly influenced by the field and demonstrate greater deviation. Examine the three mass spectrograph readings illustrated below and answer the questions that follow. Note that the upper scale of each spectrograph shows atomic mass (in amu). Below each spectrograph, the percent’s of the various isotopes present are given.

1.a. What is the molar mass of the

isotope of the element represented by spectrum A?

b. What are the name and atomic symbol of element A?

2.a. What are the symbols,

including superscripts and subscripts for the isotopes in spectrum B?

b. Based on the experimentally obtained values of atomic mass and percent abundance, calculate the average molar mass of this element.

c. Which isotope deviated most from its straight-line path?3.

a. Calculate the average molar mass of the element in Spectrum C.

Mass 30 29 28 27 26 25 24 23

Mass 30 29 28 27 26 25 24 23

11.2 10.3 78.7

Mass 56 55 54 53 52 51 50 49

2.38 9.55 83.8 4.31

b. What are the symbols, including superscripts and subscripts, of the isotopes of this element?

c. Which isotope deviated the least from its straight-line path?

4. Uranium has three isotopes with the following percent abundances: 92U234 (0.0058%), 92U235(0.71%), 92U238 (99.23%). What do you expect the atomic mass of uranium to be in whole numbers (NO CALCULATIONS)? Why?

5. Boron exists in the form to two stable isotopes, boron-10 and boron-11. These occur in the abundance of 19.6 percent and 80.4 percent respectively. Calculate the average molar mass of boron.

6. Ninety-two percent of the atoms of an element have a mass of 28.0 amu, 5.0% of the atoms have a mass of 29.0 amu, and the remaining atoms have a mass of 30.0 amu. Calculate the average molar mass and identify the element.