1. NOTES 4 – Atomic Structure

2. The Idea of the Atom Democritus (~400 BC) Democritus (~400 BC) Greek philosopherGreek philosopher “All matter is made of tiny, indivisible particles”“All matter is made of tiny, indivisible particles” A tomos means unable to be divided A tomos means unable to be divided Democritus thought atoms were the smallest pieces of matter Democritus thought atoms were the smallest pieces of matter

3. The Development of the Modern Atomic Model John Dalton (1803) John Dalton (1803) Each element has different size and shape atomsEach element has different size and shape atoms Atoms of different elements combine to form compoundsAtoms of different elements combine to form compounds JJ Thompson (1897) JJ Thompson (1897) Atoms are solid masses of smaller charged particles, half are positive and half are negativeAtoms are solid masses of smaller charged particles, half are positive and half are negative

4. The Development of the Modern Atomic Model Ernst Rutherford (1905) Ernst Rutherford (1905) Gold Foil ExperimentGold Foil Experiment Most of the atom is empty spaceMost of the atom is empty space There is a tiny bunch of positively charged particles in the center of an atomThere is a tiny bunch of positively charged particles in the center of an atom

5. The Gold Foil Experiment

6. The Development of the Modern Atomic Model Niels Bohr (1911) Niels Bohr (1911) Negatively charged particles orbit the bunch of positively charged particlesNegatively charged particles orbit the bunch of positively charged particles The orbiting, negative particles are organized into energy levelsThe orbiting, negative particles are organized into energy levels

7. The Modern Atomic Model

8. Subatomic particles – tiny particles that make up atoms Subatomic particles – tiny particles that make up atoms There are three types of subatomic particles: There are three types of subatomic particles: 1.Protons (p + ) – positively charged particles 2.Neutrons (n 0 ) – particles with no charge 3.Electrons (e - ) – negatively charged particles

9. Nucleus Nucleus - the dense center part of the atom Nucleus - the dense center part of the atom Contains the protons and neutronsContains the protons and neutrons Nucleus contains 99.99% of the mass of an atomNucleus contains 99.99% of the mass of an atom Electrons orbit nucleusElectrons orbit nucleus

10. Atoms are extremely small

11. Comparing Subatomic Particles ParticleLocationSize & MassCharge Proton (p + )Nucleus Equal to Neutron Positive (+) Neutron (n 0 )NucleusEqual to ProtonNeutral (0) Electron (e - )Outside Nucleus 10,000X smaller than protons and neutron Negative (-)

12. Atoms are Neutral Every atom has equal numbers of protons (p + ) and electrons (e - ) Every atom has equal numbers of protons (p + ) and electrons (e - ) Ex. Oxygen atoms have 8 p + and 8 e - Ex. Oxygen atoms have 8 p + and 8 e - The negatives cancel out the positives The negatives cancel out the positives 8 protons = + 8 charge8 protons = + 8 charge 8 electrons =- 8 charge8 electrons =- 8 charge Total charge = 0Total charge = 0

13. Count the protons and electrons in this fluorine atom

14. Electrons in Energy Levels Electrons surround the nucleus in energy levels Electrons surround the nucleus in energy levels The number of energy levels depends on how many electrons the atom has The number of energy levels depends on how many electrons the atom has

15. How Many Electrons in Each Level? 1 st energy level holds 2 e - 1 st energy level holds 2 e - 2 nd energy level holds up to 8 e - 2 nd energy level holds up to 8 e - 3 rd energy level holds up to 18 e - 3 rd energy level holds up to 18 e - Atoms with 2 e - or less have 1 energy level Atoms with 2 e - or less have 1 energy level Atoms with 3 to 10 e - have 2 energy levels Atoms with 3 to 10 e - have 2 energy levels Atoms with more than 10 e - have at least 3 energy levels Atoms with more than 10 e - have at least 3 energy levels

16. Valence Electrons Valence electrons - The electrons in the outer most energy level Valence electrons - The electrons in the outer most energy level Valence electrons determine the reactivity of an atom Valence electrons determine the reactivity of an atom Will it bond with other atoms?Will it bond with other atoms? Ex. Oxygen atoms have 8 electrons Ex. Oxygen atoms have 8 electrons 2 in the first level2 in the first level 6 in the second level6 in the second level How many valence e- does an oxygen atom have?How many valence e- does an oxygen atom have? 6

17. The periodic table gives information about 1 atom of any element

22. Atomic Number = Number of protons & electrons Atomic Number = Number of protons & electrons Ex. 1 oxygen atom has 8 protons and 8 electrons Mass Number = Number of protons + neutrons Mass Number = Number of protons + neutrons Ex. 1 oxygen atom has 16 protons + neutrons To figure out the # of neutrons, subtract the atomic number from the mass number 16 – 8 = 8 so an oxygen atom has 8 neutrons

23. How many protons, neutrons, and electrons are in one atom of sodium? Atomic number is 11, so there are: Atomic number is 11, so there are: 11 protons 11 electrons Mass number is 23, so there are: Mass number is 23, so there are: 23 – 11 = 12 12 neutrons