Chemistry 8 Lesson 5: Chemical Elements
1. Summary of theory
1.1. What is a chemical element?
A chemical element is a collection of atoms of the same type that have the same proton in the nucleus.
b. Chemical symbol
– Chemical symbols to represent chemical elements briefly.
– Each chemical element is represented by 1 or 2 letters. In which the first letter is written in capital letters called chemical symbols.
How to write chemical symbols:
The first letter is capitalized. For example: Carbon: C, hydrogen: H, oxygen: O.
+ The second letter, if any, is in lower case. For example: Iron: Fe, Sodium: Na, Calcium: Ca.
Each element symbol has only one atom of that element left.
1.2. Atomic Block
Mass atoms have a very small mass. If it is measured in grams, it has a very small value.
Mass of 1 C atom = 1.9926.10-23g
*Convention: Take 1/12 KLNT C as the atomic mass unit called the carbon unit (abbreviated as d.vC).
1đ.vC = 1/12. Atomic Mass C
*Define: Atomic mass is the mass of an atom in e.vC
1.3. How many chemical elements are there?
– There are more than 110 chemical elements.
+ 92 natural elements.
+ Remaining: artificial elements. In 2016 there were 4 new elements with temporary names: ununtrium, ununpentium, ununseptium and ununoctium. A Russian-American research team jointly discovered elements 115, 117 and 118, while Japanese researchers discovered element 113. These elements are not found in nature but are synthesized man created in the laboratory.
– The natural elements present in the Earth’s crust are very uneven.
– Oxygen is the most common element: 49.4%.
+ 9 elements make up: 98.6%.
+ The remaining element accounts for: 1.4%.
2. Illustrated exercise
2.1. Form 1: Identify the name, chemical symbol of the element
Lesson 1: Which element’s name and chemical symbol is incorrect?
A. Carbon, C.
B. Chlorine, Cl.
C. Iron, S.
D. Magnesium, Mg.
The symbol for iron is Fe .
S stands for sulfur
Lesson 2: Write the chemical symbols for the following elements:
a) Sulfur: …………
b) Zinc: …………
c) Sodium: …………………….
d) Dong: …………
e) Mercury: …………
f) Silver: ………….
The symbols for the corresponding elements are:
b) Zinc: Zn
c) Sodium: Na
d) Copper: Cu
e) Mercury: Hg
f) Silver: Ag
2.2. Form 2: Meaning of chemical formula
What do the following expressions mean?
a) O: …………
b) 2O: …………
c) 3Cu: …………
d) 5Cl: …………
a) O: one oxygen atom
b) 2O: two oxygen atoms
c) 3Cu: three copper atoms
d) 5Cl: five chlorine atoms.
3.1. Essay exercises
Question 1: Let the atomic mass of Barium be 137. Calculate the actual mass of the above element?
Verse 2: Let the mass number of element X be 39. Know that the total number of atomic particles is 58. Identify the element and give the number of neutrons?
Question 3: Let the nuclear charge of X be 15+. Know that the number of charged particles is 14 more than the uncharged. Determine the element and mass number?
Verse 4: The atom of element X has seven times the atomic mass of the atom of element hydrogen, which is the atom of any element. Give the number p and number e?
3.2. Multiple choice exercises
Question 1: How many chemical elements are there:
A. Over 110 elements
B. Exactly 110 elements
C. 111 elements
D. 100 elements
Verse 2: The symbol for the element Xecium is .
Question 3: Atomic mass
A. 1, 9926.10-24kg
Verse 4: For element O with atomic mass of 16, Mg is 24. Which atom is heavier?
A. Mg is heavier than O
B. Mg is lighter than O
C.O equals Mg
D. All the answers above
Question 5: Let an atom of element C have 11 protons. Choose the wrong answer
A. It is the element Sodium
B. The number of e is 16 e
C. Atomic mass is 22
D. Stt in the periodic table is 11
Through this lesson, you will learn:
- Concept of atomic mass and atomic mass of some chemical elements in table 1 (sgk/42)
- Know how to calculate and compare the atomic mass of one element with another
- Know the tables, find the atomic mass of a particular element