Ch 7. Understanding the atom & Ch 8. elements and chemical bonds

1. Ch 7. Understanding the atom&Ch 8. elements and chemical bonds KMS 8th grade science

2. The atom • The smallest piece of an element that still represents that element. • The atom is made up of main parts two Electron Cloud Nucleus

3. The nucleus • A small area in the center of an atom • Responsible for most of the atom’s mass • Contains positive charge • Contained in the nucleus: protons neutrons

4. PRotons • An atomic particle that has a positive charge • Size: • Charge: • Location: • Atomic Mass Unit (amu) = Larger than electrons Positive Nucleus 1 amu

5. Neutrons • Neutral particle that exists in the nucleus of an atom. • Size: • Charge: • Location: • Atomic Mass Unit (amu) = Larger than electrons (about the same size as a proton) Neutral Nucleus 1 amu

6. The electron cloud • The area around an atomic nucleus where an electron is most likely to be located • Contained in the electron cloud: electrons

7. electrons • A particle with a negative charge. • Size: • Charge: • Location: • Atomic Mass Unit (amu) = Much smaller than protons and neutrons Negative Electron Cloud 1/1,840 amu

9. Contributors • Democritus (pg. 236) • Aristotle (pg. 236) • John Dalton (pg. 236) • J.J. Thomson (pg. 238) • Ernest Rutherford (pg. 240) • James Chadwick (pg. 245) • Niels Bohr (pg. 245)

10. Democritus • Proposed that different types of matter are made from different types of atoms. • Proposed that space between atoms was “empty”

11. Aristotle • 384 – 322 B.C. • Did not believe in Democritus’ idea that between atom’s were empty space • He believed all matter was made of fire, water, air and earth.

12. John dalton • Late 1700’s • All matter is made of atoms that cannot be created, divided or destroyed. • Atoms of the same element have the same mass and are exactly alike

13. j.j. thomson • 1897 • Found negatively charged particles (electrons) and reasoned that they must have a positive charge that balances them out.

14. Ernest Rutherford • Thomson’s student • First atomic model with nucleus • Came up with the word proton for positive charge

15. James chadwick • Discovered the neutron • Completed the atomic model

16. Nielsbohr • Proposed that electrons move in circular orbits, called energy levels, around the nucleus.

17. elements • Pure substance made of only one type of atom • A substance made from atoms that all have the same number of protons. In the empty box in your notes, look at the periodic table and fill out an element box for carbon

18. Carbon element box Element Atomic Number Carbon 6 C Symbol Atomic Mass 12.01

19. Atomic number • The number of protons located in the atom’s nucleus. • Turn to the periodic table in your text book…can you find the atomic number in the following element boxes? • Oxygen • Potassium • Gold

20. Protons and neutrons protons • The number of of the same element will always be • However, atoms of the same element can have • For example: every carbon atom has 6 protons, however some have 6, 7, or 8 neutrons. the same a different number of neutrons

21. These are called… • Isotopes - atoms of the same element that have different numbers of neutrons. • Most elements have isotopes. several

22. Mass number • The sum of protons and neutrons in an atom. Average atomic mass • The average mass of the element’s isotopes, weighted according to the abundance of each isotope.

23. The average atomic mass is and based on each isotope’s • Approximately 99% of Earth’s carbon is which is why carbon’s average atomic mass is close to 12 (12.01) weighted abundance on Earth Carbon-12

24. The arrangement of elements Dmitri Mendeleev (1834-1907) • Arranged by: • Arranged in order of: • Periodic- Increasing atomic mass Describes something that occurs or repeats in regular intervals.

25. Metals, nonmetals, or metalloids The three main regions of elements on the periodic table classify elements as

26. Columns • The (up and down) columns of the periodic table are called • There are groups • Elements in the same group or family have vertical groups or families 18 Similar chemical and physical properties

27. Rows • The horizontal rows of the periodic table are called • Elements in a period • The first element in a period is usually an active , and the last element in a period is always an inactive . periods are not alike in properties solid gas

28. Rows • Atomic number (number of protons) • Atomic mass (number of protons + neutrons) • Metals are on the • Non-metals are on the increases from left to right across a period increases from left to right across a period left right

29. Energy levels • Different electrons within an atom have • An electron moves around the nucleus at a distance that corresponds to • Electrons to the nucleus have the amount of energy. • Electrons from the nucleus have the energy. different amounts of energy the amount of energy it has. closest least furthest most

30. Electron Energy Levels

31. Energy levels electrons • Negatively charged are strongly attracted to charged nucleus of an atom. • These OUTERMOST electrons can easily be attracted to the nucleus of • We call these OUTERMOST electrons positively other atoms valence electrons

32. Energy levels • Valence Electrons - outermost electron of an atom that participates in chemical bonding. • These attractions are what cause chemical bonds

33. How to determine the number of valence electrons valence electrons • The number of in each atom of an element can help determine • The exception to finding number of valence electrons is the type and the number of bonds it can form helium

34. Group #/Valence electron 1 valence electron • Group 1 • Group 2 • Group 3-12 • Group 13 • Group 14 • Group 15 • Group 16 • Group 17 • Group 18 • Helium is the exception and has V.E. 2 valence electron valence electrons vary 3 valence electrons 4 valence electrons 5 valence electrons 6 valence electrons 7 valence electrons 8 valence electrons 2 **go back to the periodic table in your notes and label the valence electrons.