CH4:Atoms II- LCHS Physical Science

Chapter 4: Atoms II - LCHS Physical Science

Objectives: The learner will...

...describe the organization of the Periodic Table
...identify isotopes of various elements
....define atomic mass and weight (average atomic mass)

Vocabulary:

metal : elements that typically give up electrons in ionic bonds
non-metal : elements that typically receive electrons in ionic bonds
metalloid : elements that will give or receive electrons during chemical bonding (B, Si, Ge, As, Sb, Te, Po, At)
atomic mass : the sum of a single atom's protons and neutrons in amu's
atomic weight : the average weight of all the naturally occuring isotopes of an atom
isotope : elements that are chemically identical in every respect except number of neutrons

PERIODIC TABLE ORGANIZATION

The periodic table is arranged in increasing order of ATOMIC NUMBER (Z). Dmitri Mendeléev (1834-1907) is first credited with arranging the known elements of his time into a table (based on atomic mass). METALS are on the left side of the table (except for Hydrogen), NON METALS are on the right, and METALLOIDS are sandwiched between the metals and non metals.

METALS are typically shiny, malleable (can be hammered into thin sheets), good conductors (heat and electricity), and readily donate electrons in chemical reactions. Most elements are metals ("givers" rather than "receivers" of electrons) .

NON METALS are typically nonlustrous, brittle, poor conductors and readily accept electrons in chemical reactions.

METALLOIDS (B, Si, Ge, As, Sb, Te, Po, At) have properties of both metals and non-metals, e.g. silicon (Si) is shiny, brittle and can insulate or conduct electricity (metalloids are used to make semiconductors, i.e. transistors).

The most reactive metals are on the lower-left of the table (Francium). Ignoring the far right column of nobel gases, the most reactive non-metals are on the upper right of the table (Flourine).

	1	2		3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
1	1 H																		2 He
2	3 Li	4 Be												5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg												13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca		21 Sc	22 Ti	23 V	24 Cr	25 Mn	26 Fe	27 Co	28 Ni	29 Cu	30 Zn	31 Ga	32 Ge	33 As	34 Se	35 Br	36 Kr
5	37 Rb	38 Sr		39 Y	40 Zr	41 Nb	42 Mo	43 Tc	44 Ru	45 Rh	46 Pd	47 Ag	48 Cd	49 In	50 Sn	51 Sb	52 Te	53 I	54 Xe
6	55 Cs	56 Ba	*	71 Lu	72 Hf	73 Ta	74 W	75 Re	76 Os	77 Ir	78 Pt	79 Au	80 Hg	81 Tl	82 Pb	83 Bi	84 Po	85 At	86 Rn
7	87 Fr	88 Ra	**	103 Lr	104 Rf	105 Db	106 Sg	107 Bh	108 Hs	109 Mt

*Lanth			*	57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb
**Act			**	89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No

FAMILIES

Vertical columns in the periodic table are called groups or families because they share similar chemical and physical properties.

Group/column	Family Name	members
1	Alkali Metals	H, Li, Na, K, Rb, Cs, Fr
2	Alkaline Earth Metals	Be, Mg, Ca, Sr, Ba, Ra
3 - 12	Transition Metals and Inner Transition (Lanthanoid and Actinoid Series) Rare Earth Metals	see periodic table most popular family is Cu, Ag, Au Copper. Silver, Gold

13	Boron Group	B, Al, Ga, In, Tl
14	Carbon Group	C, Si, Ge, Sn, Pb
15	Nitrogen Group	N, P, As, Sb, Bi
16	Oxygen Group	O, S, Se, Te, Po
17	Halogens (Salt Formers)	F, Cl, Br, I, At
18	Noble Gases (inert) Won't form stable compounds	He, Ne, Ar, Kr, Xe, Rn

ISOTOPES

Since electrons weigh so little, the atomic mass of an atom is simply the number of protons plus neutrons. Any 2 atoms of the same element will be chemically identical in every respect but can vary in atomic mass. Since they have to be identical in terms of atomic number (protons) it is the number of neutrons that varies slightly. These variations of neutrons in the same element are called isotopes. Carbon can have 6, 7 or even 8 neutrons, going by the isotope symbols of C-12, C-13, and C-14 respectively. C-12 (6 protons + 6 neutrons) is the most common. C-14 is radioactive and is used to date fossils.

ATOMIC WEIGHT

If you look on the detailed Periodic Table you will see that the average mass of Carbon is 12.011. This average is calculated by taking a large random sample of carbon atoms and averaging all their isotope masses (e.g. how would you find the average weight of everyone in class?). If you picked 1000 Carbon atoms at random you might find 990 C-12, 8 C-13 and 2 C-14.
So [(990 x 12)+(8 x 13)+(2 x 14)]÷1000
or [(11880)+(104)+(28)]÷1000 = 12.012
The bigger and more random our sample, the closer our average of all 3 naturally occuring isotopes will equal 12.011.

TRY THIS ONLINE PERIODIC TABLE QUIZ

Practice:

Help:

PB1
If a N atom has 6 neutrons what is its mass?

A=Z+N

PB2
How many neutrons does an isotope of S - 33 have?

A=Z+N
33=16+N
33-16=N

PB3
What is the average mass (amu) of Ga?

(see periodic table)

PB4
What element has an average mass of 12.011?

(see periodic table)

PB5
How many protons does the element have with an average mass of 6.94?

(see periodic table)

PB6
What is the main element of the family containing Ga?

(see periodic table)

PB7
What is the mass of an isotope of Ca with 22 neutrons?

(see periodic table)

PB8
An isotope of what element has a mass of 7 and 4 neutrons?

(see periodic table)

PB9
30 atoms of O-15 and 60 atoms of O-16 have what average mass?

((30x15)+(60x16))/90

PB10
100 atoms of C-12, 10 atoms of C-13, and 5 atoms of C-14 have what average mass?

((100x12)+(10x13)+(5x14))/115

answer bank:

12.1739
17
3
42

69.735
C
Li

13
B
15.666

Scientist Spotlight:
Mendeléev, Dmitri (1834-1907) Russian chemist who arranged the 63 known elements into a periodic table based on atomic mass, which he published in Principles of Chemistry in 1869.

Resources (Study Links/Study Tips/Reading Lists)
TRY THIS ONLINE PERIODIC TABLE QUIZ

Chapter 4: Atoms II - LCHS Physical Science

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