Unit 5: Atomic Structure and the Periodic Table of Elements

1. Unit 5: Atomic Structure and the Periodic Table of Elements

2. 5.1 Atoms are the smallest form of element s • What we should already know: • All matter is made of atoms • Elements are the simplest substances • What we will learn: • Where atoms are found and how they are named • About the structure of atoms • How ions are formed from atoms

3. Greek philosophers use to believe that everything on Earth was made up of air, water, fire, and earth or a combination of those substances. • Today’s chemists know here are about 100 basic substances, or elements, which make up everything we see and touch. • Some of these elements appear by themselves • Some appear in combination with others

4. Types of Atoms in Earth’s Crust and Living Things: • Hydrogen (H) makes up about 90% of the mass of the universe • Hydrogen (H) makes up only about 1% of the earth’s crust • Look at the graphs on page 138: • Oxygen (O) makes up the majority of both humans and the earth’s crust • After oxygen (O) there are many differences in our make-up • All living things are composed primarily of: oxygen (O), carbon (C), hydrogen (H) , and nitrogen (N)

5. Names and Symbols of Elements: • Each element has its own unique atomic symbol: • Some elements use the first letter of the name: Oxygen = O Hydrogen = H Sulfur = S • Other elements use the first letter plus another letter found in the name: Aluminum = Al Platinum = Pt Zinc = Zn • Some elements use the letters from the Latin word such as: gold = Au Lead = Pb • No matter the letters used, the first letter is always UPPER CASE and the second letter is always lower case

6. Each element is made of a different atom • John Dalton proposed that each element is made of tiny particles called atoms. • All of the atoms of a particular element are identical but are different from atoms of all other elements.

7. The Structure of an Atom • Atoms contain charged particles which can be (+) or (-) • Particles with like charges repel each other (push away from) • Particles with different charges attract each other (drawn to) • Atoms are composed of three types of particles: • Protons • Neutrons • Electrons

8. Protons: • Carry a (+) charge • Are found in the nucleus of the atom • Make the element what it is • If you change the number of protons, you change the element • Neutrons: • Carry a neutral charge (no charge) • Are found in the nucleus of the atom • Have about the same mass as a proton • Electrons: • Carry a (-) charge • Are found outside the nucleus of the atom • Determine how elements will bond with each other

9. Atomic Model Electrons (-) Protons (+) Neutrons

10. Size and attraction: • About 10-10 meter in diameter • You could fit millions of atoms in the size of the period in your book • Electrons are much smaller than protons and neutrons • About 2000 times smaller • Electrons move about the nucleus very quickly • Impossible to pin point the location at any time • Stay attracted to the nucleus because of the (+) protons

11. Atomic Number: • The atomic number of an atom indicates the number of protons in the nucleus. • You can not change the atomic number of an element and still have that same element • The atomic number of hydrogen (H) will always be 1. • The atomic number of gold (Au) will always be 79.

12. Atomic mass number • The total number of protons and neutrons in an atom’s nucleus. • Not all atoms have the same number of neutrons: • Chlorine (Cl) has 17 protons but some atoms have 18 neutrons, others may have 20. • When atoms of the same element have a different number of neutrons they are called isotopes. • To find the number of neutrons you must subtract the atomic number from the atomic mass number.

13. Ions: • A neutral atom has an equal number of protons (+) and electrons (-). • The negative charges and the positive charges balance each other. • An ion is formed when an atom loses or gains one or more electrons. • By gaining or losing electrons, the balance of (+) and (-) is no longer there.

14. Positive Ions: • When an atom loses one or more electrons, it takes on a positive charge. • Example: page 142 • A neutral atom of sodium contains 11 protons and 11 electrons—the charges balance each other. 11 (+) 11 (-) Neutral charge

15. When the sodium atom loses an electron, there are more (+) charges than (-) giving the ion a + charge • To indicate or write a positive charged atom, you add a + sign to the right side of the atomic symbol. • Na+ • If an atom loses more than one electron, you add the number lost to the atomic symbol before the + sign • Na 2+

16. Negative Ions: • Negative ions are formed opposite to the positive ions—Electrons are added to the atom giving it a negative charge. • When indicating a negative electron, you add a – sign to the top right of the atomic symbol. • Cl- • If more than one electron is added, you write the number with the sign. • Cl2-

17. 5.2: Elements make up the periodic table • Not all atoms of an element have the same atomic mass number (total number of protons and neutrons) • The atomic mass of the atom is the average mass of all the element’s isotopes (same atom-different number of neutrons.)

18. Mendeleev’s Periodic Table page 146 • Early 1800’s, Dmitri Mendeleev wanted to organize the elements based on their physical and chemical properties. • Created the first periodic table by arranging the elements by: • Similarities made up each row • Increase down each column by atomic mass

19. Modern periodic table • Page 148-149 in your book • Elements are arranged by atomic number (number of protons) • Elements with Similar properties are arranged in columns

20. Reading the periodic table • Each square represents an individual element: Atomic symbol Atomic number (number of protons) Name Atomic mass

21. The color of the letters indicates the physical state of the element at room temperature: • White = gas • Blue = liquid • Black = solid • Your table is also divided by the colors: • Green = Nonmetal • Yellow = Metal • Purple = Metalloid

22. Groups • Each column on the table is known as a group or family because they appear to be related. • The halogens-group 17 tend to combine well with groups one and two. • Similar chemical properties • Different physical properties Gases Liquid Solids

23. Periods • Each horizontal row is called a period. • Properties of the elements change in a “predictable” way from one end to the other. • Elements on the far left are metals. • Elements on the far right are nonmetals.

24. What else is on the table? An atom’s size is important because it affects how the atom will react with another atom. What is the pattern in the table for atomic size?

25. Periodic table densities: Densities of the elements follows a pattern with the least dense on the left and right and the most dense in the middle.

26. 5.3: The periodic table is a map of the elements • Just like a map of the United States, the periodic table is a map showing: • Metals (left) • Metalloids (middle) • Nonmetals (right) • Nonmetals does not count hydrogen (H) • Your book shows these regions in: • Yellow (metals) • Purple (metalloids) • Green (nonmetals)

28. Reactive: • Indicates how likely an element is to undergo a chemical change. • Most elements are somewhat reactive and combine with other materials • Groups 1 and 17 are the most reactive • Group 18 is the least reactive

29. Metals: • Elements that conduct electricity and heat well • Have shiny appearance • Can be shaped easily by pounding, bending, or being drawn into a long wire • Solids at room temperature except for mercury • Reactive and transition

30. Reactive metals • Groups 1 and 2 • Group 1 is alkali metals • Very reactive • When exposed to air-rapid reactions occur • Sodium and potassium are stored in oil • Group 2 is alkaline earth metals • Less reactive than alkali metals • More reactive than most other metals • Calcium and magnesium

31. Transition metals • Groups 3-12 • Generally less reactive than most other metals • Properties make them useful in industry and technology • Commonly combined to form alloys such as brass (combination of copper and zinc) • Includes common metals such as copper, gold, silver, and iron

32. Rare Earth Elements • Top row of the two rows of metals that are usually separated from the rest of the table • AKA: lanthanides • Thought to be rare in amount but have been discovered as more common just hard to isolate in pure form.

33. Nonmetals • Found on the right side • Properties are generally the opposite of the metals and vary more: • Many are gases at room temperature • Some are solids • One is a liquid • Solids are dull and cannot be shaped by hammering or drawn into wires • Generally poor conductors of heat and electricity

34. Halogens: • Greek meaning “forming salts” • Group 17 • Very reactive nonmetals that form compounds called salts with many metals • Often used to kill harmful microorganisms • Noble Gases: • AKA: inert gases • Group 18 • Almost never react with other elements • Examples: neon, krypton, xenon, argon

35. Metalloids • Elements that have properties of both metals and nonmetals • Often make up the semiconductors of electrical devices • Semiconductors conduct electricity under some circumstances but not others

36. Some atoms change their identity • Radioactivity: • Process by which atoms produce energy and particles • Isotopes (atoms with different numbers of neutrons) are radioactive if the nucleus has too many or too few neutrons • When this happens, particles are produced from the nucleus of the atom to restore the balance.

37. Radioactive Decay • Radioactive decay: • When radioactive atoms produce energy and particles from their nuclei, the identity of the atom changes because the number of protons changes. • Steady rate of change • Half life: • Amount of time it takes for one-half of the atoms in a particular sample to decay. • Not affected by temperature or pressure • Specific to each isotope

38. Half life example: • 1000 atoms of kryptonite • Half life of kryptonite is 1 year • After 1 year, you would have ½ or 500 atoms of kryptonite. • After 2 years, you would have ½ of the atoms from year 1 or 250 atoms of kryptonite. • After 3 years, you would have ½ of the atoms from year 2 or 125 atoms of kryptonite.

39. Scientific notation • “short hand” way for scientists to write extremely large or small numbers. • It will always be a number between 1 and 10 and a power of 10. • To write 6,400,000,000 in scientific notation you move your decimal to the left until you end up with 6.4. • Count how many spaces you moved (9) • Re-write the number as 6.4 x 109

40. To write 0.0000023 in scientific notation: • Count how many spaces you move the decimal to the right to get to 2.3 • 6 spaces • Re-write the number as 2.3 x 10-6 • When going to scientific notation: • If you move your decimal to the left, your exponent is positive • If you move your decimal to the right, your exponent is negative

41. When going from scientific notation: • If you exponent is positive you move your decimal to the right • If your exponent is negative you move your decimal to the left.