The Periodic Table

1. The Periodic Table

2. The Periodic Table • Elements are represented by symbols. • Arranged in order based on the number of protons an atom of that element has in the nucleus. • Periodic Law: states when elements are arranged this way, similarities in their properties will occur in regular pattern.

3. History of the Periodic Table • Russian scientist Dmitri Mendeleev • Mid 1800’s - About 70 elements were known. • Wrote down the elements in order of increasing mass. • Found a pattern of repeating properties.

4. Mendeleev’s Table • Grouped elements in columns by similar properties in order of increasing atomic mass. • Found some inconsistencies - felt that the properties were more important than the mass, so switched order. • Found some gaps. • Must be undiscovered elements. • Predicted their properties before they were found.

5. The Modern Periodic Table • Elements are still grouped by properties. • Similar properties are in the same column. • Order is in increasing atomic number (first scientist to do this was Moseley). • Added a column of elements Mendeleev didn’t know about. • The noble gases had not been found because they didn’t react with anything.

6. Atomic Number • The number of protons in the nucleus of an atom.

7. Symbols: Atomic Number A Y 23 X Na Z 11

8. Mass Number • The sum of the numbers of protons and neutrons in the nucleus of an atom.

9. Symbols: Mass Number A Y 23 X Na Z 11

10. The Mass of an Atom • Atomic mass unit (amu): describes the mass of an atom or molecule; it is exactly 1/12th the mass of a carbon atom. Used because the masses of atoms are very tiny, so the numbers would be too small to work with. • Average atomic mass: weighted average that includes common isotopes.

11. Calculating the Number of Neutrons • Subtract the mass number from the atomic number.

12. A X Y Na 23 11 Z Neutrons = A – Z Example Na = 23-11=12

13. Ions • An atom, or group of atoms, that has lost or gained one or more electrons and has a negative or positive charge. • Cation: ion with a positive charge. • Anion: ion with a negative charge.

14. A X Y Na +1 23 11 Z Electrons = Z - Y Example Na = 11 – 1= 10

15. Distinguishing Between Atoms • Definition: ISOTOPE- Atoms of same element with different numbers of neutrons • Isotopes have similar chemical properties because the proton an electron counts are the same. However: Isotopes may have different physical properties such as density

16. Naming Isotopes • Put the mass number after the name of the element • carbon- 12 • carbon -14 • uranium-235

17. Isotopes of Hydrogen

18. Hydrogen makes up less than 1% of the Earth’s crust. Only 1 out of every 6000 hydrogen atoms is deuterium

19. Seventy-five percent of the mass of the sun is hydrogen, with protium isotopes outnumbering deuterium 50,000 to 1.

20. PRACTICE TIME!!!!

21. Families of Elements • Elements are classified into three groups: • Metals • Nonmetals • Semiconductors (metalloids)

22. 8A 1A • The elements in the A groups are called the representative elements 2A 3A 4A 5A 6A 7A

23. You must also tell the difference between metals, non-metals and metalloids (semi-conductors).

24. Metals • An element that is shiny and conducts heat and electricity well.

25. Every thing below and to the left of the steps, (In yellow) are metals.

26. Alkali Metals • Soft, shiny, and react violently with water.

27. Alkaline-Earth Metals • Found in limestone and the human body. • Less reactive that alkali metals, but can still react to form positive ions with a +2 charge. • Examples: calcium, magnesium

28. Group 1A are the alkali metals • Group 2A are the alkaline earth metals 1A 2A

29. Transition Metals • Much less reactive, but can form positive ions.

30. These are called the inner transition elements and they belong here. The group B are called the transition elements

31. Top row of the inner transition is called the Lanthanide series. Bottom row called the Actinide series.

32. Synthetic Elements • Man-made elements • All elements with atomic number greater than 92 are synthetic. • All radioactive

33. Nonmetals • An element that conducts heat and electricity poorly. • Most plentiful on earth.

34. Every thing above and to the right of the steps, (In purple) are non-metals.

35. Hydrogen (in white) is usually considered to be a non metal, but due to its reactivity it has its own group.

36. Semiconductors • Metalloids • An element of compound that conducts electric current better than an insulator, but not as well as a conductor does. • Only 6: boron, silicon, germanium, arsenic, antimony, and tellurium.

37. They form steps from Boron to Tellurium with Germanium and Antimony (Green) and separate the metals from non-metals.

38. Halogens • Group 17 • Highly reactive!!!

39. Noble Gases • Group 18 • Exist as single atoms. • Un-reactive. • Do not form ions!!

40. 8A • Group 7A is called the Halogens • Group 8A are the noble gases 7A

41. Periods and Groups • Periods: tells the number of electrons and their arrangement in the orbitals, horizontal rows. • Groups: Tells the number of valence electrons; vertical rows. • We will come back to this later.