chemistry periodic trends homework need done asap!!!!

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In the nineteenth century, Mendeleev used the chemical and physical properties of the elements to develop an arrangement of the elements that today we call the periodic table. In this lab activity, you will investigate how three properties of the elements—atomic radius, ionization energy, and electronegativity—vary according to atomic number. You will be making a

3

–

dimensional model of these properties for some of the representative elements, and will use it to describe and explain the trends in these properties.

Objectives

When you have completed this activity, you should be able to:

1

. Use a model to describe the trends in several physical properties of the elements.

2. Relate these trends to the electron configuration of the elements.

Materials

· small plate

· scissors

· ruler

· plastic straws, 3 colors

· calculator

· ruler

· forceps

· plastic wrap

· periodic table

Procedure

1. You will prepare a 3-dimensional model for each of the properties of the elements.

2. In order to make the 3-D model, you need to cut the straws to scale so their heights represent the relative values for each element. On the Data Table provided, convert the values for your assigned property to a scale in centimeters by using the conversion factors given below. Round your answers to the nearest tenth of a centimeter. An example is given for each property.

Property

Conversion

F

actor

Example

(For

H

ydrogen)

Atomic radius

1 cm =

30 pm

32

pm x 1 cm =

1.0

7

cm (1.1 cm)

30 pm

Ionization Energy

1 cm =

4

00 kJ

13

12

kJ x 1 cm =

3.2

8

cm (3.3 cm)
400 kJ

Electronegativity

1 cm =

0.8

unit

2.2

units x 1 cm = 2.7

5

cm (2.8 cm)
0.8 unit

3. Use the diagram of the well plate provided below to plan the placement of the elements. Your well plate should be oriented to correlate with the elements of the periodic table. Row 1 represents the first period, with well H1 as Hydrogen and well A1 as

He

lium. Row 2 represents the second period, with well H2 as

Li

thium and well A2 as

Ne

on. Rows 3 and 4 contain the elements in periods 3 and 4, omitting the transition elements.

Write the symbols for the elements in the circles.

4.

Se

lect colored straws to represent one of the three properties.

5. Place the well plate template with tape onto the bottom of the plate. Wrap the plastic wrap over the top of the plate. Make sure it is secure on the bottom and is tight across the top of the plate.

6

.

Ca

refully measure and cut a piece of straw for each element. Following the diagram you completed in Procedure 3, insert each piece into the plastic wrap.

7. Repeat steps 5 and 6 for each of the remaining two properties.

Analysis

1. Examine your tray. How do the properties change as you look from top to bottom within a group or family?

Atomic radius

Ionization energy

Electronegativity

2.

As

you look from left to right across the periodic table, how do the properties change?

Atomic radius

Ionization energy

Electronegativity

3. Write the electron configuration for the following alkali metals (Group 1).

Li

Na

K

In what way are the electron configurations for group 1 similar?

How do the electron configurations differ as you move down group 1?

4. Write the electron configuration for the elements in period 2, from Li to Ne.

Li

B

e

B

C

N

O

F

Ne

What do all the electron configurations above have in common?

How do these electron configurations differ? How does the number of protons differ?

5.
In terms of electron configuration, explain the trend in atomic radius.

Down a group

Across the period from left to right

6. In terms of electron configuration, explain the trend in ionization energy.

Down a group
Across the period from left to right

7.
In terms of electron configuration, explain the trend in electronegativity.

Down a group

Across the period from left to right

8. Look at your model again. Why do you think we say that the properties of the elements are “periodic”?

9

. On the diagram of the periodic table below, draw and label arrows that show the direction in which the three properties (atomic radius, ionization energy, and electronegativity) increase.

10

. Some of the elements show exceptions to the trends. Look at your model and select an element that seems to have an unusual value for one of these properties. Try to explain why this happens by writing the electron configuration for this element and looking for a definite change from the element before it.

11

. Write a paragraph explaining why atomic radius, electronegativity, and ionization energy show periodic trends.

Li

–

Na

1.6

2.2

98

–

K

1.0

32

2.0

2.2

2.5

3.0

112

–

PROPERTIES OF REPRESENTATIVE ELEMENTS
Element	Atomic number	Atomic radius (pm)	Straw Length (cm)	Ionization Energy (kJ/mol)	Straw Length (cm)	Electronegativity (units)	Straw length (cm)
H	1		32	1 31 2			2.2
He	2	50	23 72				–
3	15 5	5 20		1.0
Be	4		112	900		1.6
B	5		98	801		2.0
C	6	91	1086		2.5
N	7	92	14 02		3.0
O	8	73	1314	3.5
F	9	72	16 81	4.0
Ne	10	71	2081
11	19 0	496	0.9
Mg	12	160	738	1.3
Al	13	143	578
Si	14	132	786	1.9
P	15	128	1012
S	16	127	1000	2.6
Cl	17	99	1251	3.2
Ar	18	1520
19	2 35	419	0.8
Ca	20	197	590
Ga	31	141	579	1.4
Ge	137	762
As	33	139	944
Se	34	140	941
Br	35	114	1140
Kr	36	1351

PRE-LAB: PERIODIC TRENDS

1. Which groups of the periodic table contain the “representative elements”?

Why do you think these elements are called “representative”?

2. What is a periodic trend?

3. Consult a chemistry textbook to find the definitions for the following properties, then restate the definition in your own words.

Atomic radius
Ionization energy
Electronegativity

4. Read the procedure for this activity. What is the purpose for including drinking straws in the materials list?

5. Follow the directions in Procedure Step 2 to calculate the straw length needed to represent:

The atomic radius of oxygen

The ionization energy of neon

The electronegativity of arsenic

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