1. Chapter 5 Atoms: Building Blocks of Matter

2. Evidence Direct evidence is when you do something to gather the evidence Examples are Doing an experiment Reading a book Indirect evidence is when you do not see or touch the subject Examples are Hearing from someone else

3. The Greek Model All elements could be seen and touched No element was smaller then what could be seen The four elements are fire, earth, wind and water

4. Democritus Called the Greek model (over 2000 years ago) Named the smallest piece of matter the atom From the Greek word atomos meaning not to be cut Atomists – the philosophers who agreed w/ Democritus Hypothesis – small hard particles made up of same material in all shapes and sizes, never ending amount, always moving, capable of joining together

5. Dalton’s Model John Dalton (Early 1800’s) Atomic Theory All elements are composed of atoms, atoms are indivisible and indestructible particles Atoms of the same element are exactly alike Atoms of different elements are different Compounds are formed by joining of atoms of two or more elements Became foundation of atomic theory

6. Thomson’s Model J.J. Thomson (1897) Discovered that a particle smaller then the atom had to exist These were negatively charged particles - electron Plum Pudding model Atom was made up of a pudding like positively charged material throughout which negatively charged electrons were scattered

7. Thomson’s Model Raisin Pudding

8. Rutherford Ernest Rutherford (1911) Conducted an experiment in which some positive particles went through gold foil and others bounced off Proposed that atoms have a small positively charged center - nucleus All the positively charged particles are found in the nucleus and all the negatively charged electrons were scattered outside the nucleus around the edges

9. Rutherford’s Model

10. Bohr Model Niels Bohr (1913) Wanted to know where Rutherford’s electrons were located – believed that the negative and positive particles were held together because of their attraction Bohr placed each electron in a specific energy level Electrons move around in definite orbits around the nucleus – these orbits are located certain distances from the nucleus

11. Bohr’s Model

12. Wave Model Wave mechanics – today’s atomic theory is based from wave mechanics Electrons – do not move about the atom in a definite pattern - it is actually impossible to predict the location of the electrons An atom has a small positively charged nucleus surrounded by a large region where electrons are making the atom neutral – this region is mostly empty space

13. Atom Composed of subatomic particles – particles smaller than an atom Proton – positively charged particles Neutron – no charge Electrons – negative charge Nucleus – center of the atom

14. Modern Atom

15. Nucleus The core of the atom Contains 99.9 percent of the mass of the atom but is smaller then the entire atom Protons and neutrons located in the nucleus Unit of measurement for subatomic particles is Atomic Mass Unit - amu

16. Atomic Number The number of protons in the nucleus is called the atomic number The atomic number identifies the element This number will never change

17. Mass All atoms have a mass number The mass number of atom is the sum of the protons and neutrons The number of protons is the atomic number so if you have the mass of an element you can find the number of neutrons that make up the mass Uranium 235 – proton number is 92 – neutron number is 143 Mass number 9, atomic number 4 – what is the # of neutrons Atomic Mass – the average mass of all isotopes that occur naturally for that element

18. Isotopes Atoms of the same substance that have the same number of protons but different numbers of neutrons are called isotopes. name symbol A Z neutrons nitrogen-12 isotope 12 7 5 nitrogen-13 isotope 13 7 6 nitrogen-14 isotope 14 7 7 nitrogen-15 isotope 15 7

19. Electrons Electrons are negatively charged and have an amu of.0006 The exact location of a electron is not known The location in which the electron can be found is the electron cloud The electrons seem to be locked into a certain area based on its energy level

20. Energy Levels Represents the likely location for an electron in the electron cloud Electrons with the lowest energy are found in levels near the nucleus The higher the energy of the electron the farther away from the nucleus Each energy level can only hold a certain number of electrons Properties of elements depend on number of electrons in outer energy level.

21. Quark Current theory states that the different parts of the element are made up of quarks There are a number of different kinds of quarks Quarks have properties called flavor and color – there are six different flavors and three different colors

22. Forces within an atom Four forces account for the behavior of an atom Electromagnetic force – either attracts or repels particles – electrons are kept in orbit by this force Strong Force – opposes the electromagnetic force – “glues” protons together Weak force – responsible for radioactive decay Gravity – weakest force – not entirely known how it affects an atom

23. Hydrogen Atomic number of hydrogen is 1 One proton in the nucleus no neutrons

24. Review 1. Carbon 14 and carbon 12 – what is the difference? 2. What is the mass number of an element with 16 protons, 17 neutrons, and 16 electrons? 3. If an elements atomic number is 12, what does its nucleus contain? 4. How many neutrons are in an element with a atomic number of 4 and a mass number of 9?

25. Questions Go back through your notes and if there is anything you are unsure of ask now!!!!!!!!