Atomic Structure CHAPTER 4

Atoms An atom is the smallest particle of an element that retains its identity in a chemical reaction.

History Democritus (460-370BC): first suggested the existence of the atom

History John Dalton (1766-1844): proposed the Atomic Theory: 1. All elements are made of atoms 2. Atoms of the same element are identical 3. Atoms of different elements can combine to form compounds 4. Chemical reactions occur when atoms are separated, joined, or rearranged

Size of the atom One penny contains 2.4x1022 atoms of copper 100,000,000 atoms in a row would be 1 cm long Atoms can be seen with special microscopes called scanning tunneling microscopes

Atomic Structure An atom can be broken down into subatomic particles: protons, neutrons, and electrons.

Parts of an atom The nucleus is the tiny central core of an atom containing protons and neutrons Surrounding the nucleus is the electron field where electrons are located.

Protons Protons are positively charged subatomic particles located in the nucleus

Neutrons Neutrons are subatomic particles with no charge, equal in size to protons, and found in the nucleus.

Electrons Electrons are negatively charged subatomic particles, which are very small, and orbit the nucleus.

Subatomic Particles Particle Symbol Location Charge Mass (g) Electron orbital - 9.11 x 10-28 Proton p+ nucleus + 1.67 x 10-24 Neutron n0

Important Scientists J.J. Thomson (1897) discovered electrons using a cathode ray tube. Cathode Ray Video

Important Scientists Ernest Rutherford (1911) discovered protons through his gold foil experiment. Gold Foil Video

Reading and Writing in Science 1. Read pages 100-108 in the red textbook 2. Answer questions 1-14 on pages 103 and 108. Write and answer these questions in your notebooks.

Distinguishing Among Atoms Atoms of an element are different because they contain different numbers of protons. The atomic number of an element is the number of protons an atom of that element has.

Practice How many protons does each element have? Hydrogen Carbon Nitrogen Potassium Gold

Practice How many protons does each element have? Hydrogen = 1 Carbon = 6 Nitrogen = 7 Potassium = 19 Gold = 79

Mass Number The other number on the periodic table is an atom’s mass number which is the sum of protons and neutrons. What is the mass number of: Hydrogen Carbon Nitrogen Potassium Gold

Mass Number The other number on the periodic table is an atom’s mass number which is the sum of protons and neutrons. What is the mass number of: Hydrogen (1.0079) Carbon (12.011) Nitrogen (14.007) Potassium (39.098) Gold (196.97)

Neutrons To determine the number of neutrons an atom has, you subtract the atomic number from the mass number, then round to the nearest whole number. How many neutrons are found in: Hydrogen Carbon Nitrogen Potassium Gold

Neutrons To determine the number of neutrons an atom has, you subtract the atomic number from the mass number, then round to the nearest whole number. How many neutrons are found in: Hydrogen = 0 Carbon = 6 Nitrogen = 7 Potassium = 20 Gold = 118

Electrons In a neutral atom, the number of electrons is equal to the number of protons, which is equal to the atomic number. How many electrons does each atom have? Hydrogen Carbon Nitrogen Potassium Gold

Electrons In a neutral atom, the number of electrons is equal to the number of protons, which is equal to the atomic number. How many electrons does each atom have? Hydrogen = 1 Carbon = 6 Nitrogen = 7 Potassium = 19 Gold =79

Determining subatomic particles Number Protons Atomic Number Electrons Neutrons Atomic mass – atomic number

Isotopes Isotopes are atoms that have the same number of protons but different numbers of neutrons (and therefore different mass numbers).

Isotopes The most well known isotope is Carbon-14. Regular Carbon is called Carbon-12, because its mass number is 12, and it has 6 neutrons. Carbon 14 has 8 neutrons (14-6). Isotopes can be used in archeology, botany, oncology, radiology, and research.

Getting to know the Periodic Table Complete the activity to help you get to know the elements of the periodic table. This is homework if you don’t finish it. You will need to use your textbook and probably the Internet to research the periodic table and complete this activity.

History of Atomic Models Over time, scientists proposed different models of atoms, each better than the last. Thomson said it was like “plum pudding” with positive protons scattered about. Rutherford said that positive protons were in the nucleus, and electrons orbited it.

Atomic Models Bohr stated that the nucleus had positive protons, and electrons orbited in fixed shells.

Atomic Models Schrodinger proposed the quantum mechanical model, which is still used today. It states that there are protons and neutrons in the nucleus, which is surrounded by an electron cloud showing the probability of electron location.

Electrons Electrons are found outside the nucleus in shells/orbitals/energy levels.

Energy Levels The number of electrons allowed in each energy level is: Energy Level (n) Maximum Number of Electrons 1 2 8 3 8 or 18 4 18 or 32

Placing electrons Each energy level must be full before electrons can be placed in the next level up. Example: Draw an atom of Lithium

Lithium

Practice Draw an atom of Sodium.

Sodium

Practice In your notebooks, draw the first 36 atoms. Name each one, and place the correct numbers of protons, neutrons, and electrons in each. Next, research one way each of the 36 elements is used in real life and add it to your diagram (one sentence per element).