Chapter 3 Chemical Foundations: elements, atoms, and ions

1. Chapter 3Chemical Foundations:elements, atoms, and ions

2. The building blocks of life and the changes they undergo are unbelievably important and a great source of curiosity • The concept of atoms being the building blocks of all matter began centuries ago (ancient India and Greece)

3. In the 17th century Robert Boyle (the first modern chemist) stressed the importance of scientific investigation • He argued that an element is anything that could not be broken down (not air and water, etc.)

4. The Elements • How many elements do we know of? • 88 are naturally occurring • They make up everything in the known universe How would you like to memorize the periodic table? Need help?

5. Only a few of these elements make up most of Earth and your body

6. Note: Even though oxygen is the clear winner in both places, it is mostly wrapped up in compounds and molecules (such as iron oxide and H2O) • Clarification:“Element” can be used to refer to: • a single atom • a sample (as in air contains the element oxygen) • generically (as in the body contains the element sodium)

7. Symbols for the Elements • Most names of elements come from Greek, Latin, and German • example: Gold was called aurum (Latin) meaning the dawn • Bromine comes from brwmoV, Greek for stench • Some named for places or people (e.g. plutonium for Pluto, Einsteinium for Einstein)

8. Usually names are abbreviated called symbols • First letter ALWAYS capitalized • second letter, if there is one, is not • sometimes the original Greek or Latin is preserved in the symbol if not the name (e.g. gold is Au)

10. Dalton’s Atomic Theory • In the 1700s people knew: • most natural things were really mixtures • pure substances are either elements or compounds • a compound is made of the same ratio of stuff no matter where it comes from (law of constant composition) • John Daltonin early 1800s knew this and developed his theory…

11. Dalton’s Atomic Theory • Elements are made of tiny particles called atoms. • All atoms of a given element are identical. • The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative weights.

12. Dalton’s Atomic Theory • Atoms of one element can combine with atoms of other elements to form chemical compounds; a given compound always has the same relative numbers of types of atoms. • Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.

13. his model explained a lot and even predicted the existence of other chemicals (like these)

14. Formulas of Compounds • Chemical formulas tell you what and relatively how many atoms are in a compound

15. Rules for writing formulas • Each atom present is represented by its element symbol • The number of each type of atom is indicated by a subscript written to the right of the element symbol • If only one element of a given type is present, the subscript 1 is not written

16. The Structure of the Atom • In Dalton’s time scientists believed elements were made of atoms, and compounds were atoms somehow held together • but what is an atom? • took nearly 100 years to figure it out!

17. Thomson’s Experiment JJ Thomson (of Cambridge University) 1890s

18. Thomson’s Experiment • Thomson experimented with a cathode ray tube • He discovered electrons, determined they had negative charge and calculated their speed and mass

19. The Plum Pudding model • Thomson imagined the atom as a positively charged cloud filled with electrons called the Plum Pudding Model positive cloud + electrons = neutral atom

20. Plum pudding…

21. Rutherford’s experiment • Ernest Rutherford’s work changed the plum pudding model • he liked shooting “alpha” particles through things to see what would happen • so he shot some through really thin gold foil…

22. to his great surprise, the positive alpha particles didn’t all plough right through! • some were deflected! • implying there was some positive area in the atom that was deflecting the positive alphas

23. this is what should have happened if plum pudding model was correct • Rutherford said since most made it, but some strongly deflected so that the atom looks like…

24. Rutherford’s work gave us the nuclear atom (one with a nucleus)

25. Rutherford reasoned that hydrogen has just one proton with one electron buzzing around it • also reasoned that other atoms just had more protons and electrons • by 1932, a neutral particle - the neutron - was discovered in the nucleus

26. Introduction to the Modern Concept of Atomic Structure • today’s model looks something like this • ultra-small nucleus • atom is about 100,000 times bigger than the nucleus! • like a grain of sand in the middle of the stadium