Atoms

Elements of periodic table

1. Atomic Theory Atoms

2. Greek Philosophers Aristotle 4 Elements of matter -Earth -Fire -Air -Water

3. Matter is made of atoms (cannot be further divided), the word atom comes from the Greek word “ atomos ” which means indivisible. Democritus

4. Atoms were tiny particles that could not be divided John Dalton proposed that an atom is a sphere of matter that is the same throughout and can’t be seen by human eyes Marble Model John Dalton

5. Came up with the idea of the electron negatively charged particle Thomson discovered that all atoms contain electrons, which are tiny, negatively charged particles. Thomson proposed that an atom is a sphere of positive charge. The electrons are mixed uniformly in the sphere . Cookie Model Thomson

6. Ernest Rutherford He hypothesized that almost all the mass and all the positive charge of an atom is concentrated in an extremely tiny nucleus at the center of the atom.

7. Thought electrons traveled in fixed paths around the nucleus called energy levels . Bohr

8. Atomic Structure Arrangement and number of sub-atomic particles Protons Neutrons Electrons

9. Center or core of an atom Contains 99.9% of the weight of an atom Contains protons and neutrons Nucleus

10. Positively Charged Sub-atomic particles Found in the nucleus All protons are a like Proton

11. Neutrally charged (no charge) sub-atomic particle Found in nucleus Neutrons

12. They are the negatively charged particles orbiting the nucleus. It is much smaller than the protons and the neutrons . Electrons

13. What is the net charge of the atom ? The atom is formed of positively charged proton in the nucleus and negatively charged electrons in the energy level ,but they are equal to each other in number ,making the net charge of the atom “neutral”. No of positive protons = No of negative electrons

14. They are charged atoms N umber of positive protons = Number of negative electrons. Ions Positive ion Negative ion

15. If the atom lost an electron ,therefore the number of positive protons are more than the negative electrons making the atom positively charged Positive Ion

16. If the atom gained an electron ,therefore the number of negative electrons are more than the positive protons making the atom negatively charged Negative Ion

17. Atomic number is the number of Protons in an atom All atoms of a particular element have the SAME number of protons (All Carbon atoms have 6 protons) In a neutral atom, T he atomic number =The number of electrons Atomic Number

18. Also called atomic weight or Mass Number Sum weight of protons and neutrons in an atom Mass Number

19. Calculate the mass number of each of the following atoms

20. O 8 16 Atomic number Mass number Symbol Oxygen Name Atomic number= Number of protons= Number of electrons Mass number= Number of protons + Number of neutrons

21. Calculating Neutrons: Mass number = protons + neutrons so….. Neutrons = mass number – protons What is the number of neutrons of the following atom ? A 21 45

22. In 1869 Dimitri Mendeleev was working on a way to classify elements. At the time, more than 60 elements had been discovered. And he arranged the elements according to their atomic mass Developing a Periodic Table

23. 100 table The periodic table is a chart of the elements arranged according to their atomic number in rows and columns according to their physical and chemical properties.

24. Symbol

25. The periodic table is a chart of the elements arranged into rows and columns according to their physical and chemical properties. It can be used to determine the relationships among the elements . What is the periodic table?

26. Groups and Periods Columns in the periodic table represents “groups” There are 18 groups in the periodic table. Elements of the same the same group have the same chemical properties as the all have the same number of electron/s in the outer most energy levels.

27. Rows in the periodic table represent “periods”. There are 7 periods in the periodic table . Elements of the same period have the same number of energy levels

28. The Periodic Table of Elements

29. Periodic Table A great deal of information about an element can be gathered from its position on the period table. Understanding the organization and plan of the periodic table will help you obtain basic information about each of the 118 known elements.

30. Mass Number Atomic Mass (Mass Number) is the number ……………. __________ Atom p + n e - Mass # Oxygen - 8 - 33 42 - 31 15 ___ ___ ___ ___ ______ ___ ___ ___ ______ ___ ___ ___

31. Recall - How are P, N, e - related? atomic number = # protons # protons = ……………. # protons + # neutrons = atomic mass # neutrons = ……………. …………….

32. How many protons, neutrons and electrons are found in an atom of Cs ? _____________ ……………. ……………. Therefore, # Neutrons = ……………. _____________ _____________ 55 Cs 133 Example 1

33. Na Sodium 23 11 ___________ ___________ ___________

34. Example 2 If an element : Magnesium number of protons number of neutrons number of electrons complete symbol =_____________ = _____________ = _____________ _____________

35. Periodic Table

36. Metals

37. Properties of Metals Metals appear to the left of the dark ziz-zag line on the periodic table. Most metals are solid at room temperature.

38. Properties of Metals Metals have luster . This means they are shiny

39. Properties of Metals Ductile metals can be drawn into wire.

40. Properties of Metals Malleable metals can be hammered into sheets

41. Properties of Metals Metals have a high melting point . They are also very dense .

42. Properties of Metals Conductors Metals are good conductors of electricity and heat

43. Nonmetals

44. M etalloids They are the elements found along the step like line between metals & non-metals of the periodic table. (Boron “B” – Silicon “Si” – Arsenic “As” – Antimony “ Sb ” – Tellurium “ Te ” – Polonium “Po” – Astatine “At”)