Understanding Symbols, Formulae, and the Law of Conservation in Chemistry SS 1 First Term Lesson Notes Week 5
Chemistry SS 1 First Term Lesson Notes – Week 5
Subject: Chemistry
Class: SS 1
Term: First Term
Week: 5
Age: 14-16 years
Topic: Symbols, Formulae, and Equations I
Sub-Topics:
- Chemical Symbols of Elements
- Valency: Definition, Valencies of Elements and Radicals, Writing Formulae
- Empirical and Molecular Formulae
- Law of Conservation of Matter
Duration: 40 minutes
Behavioral Objectives:
By the end of the lesson, students should be able to:
- Identify chemical symbols for common elements.
- Define valency and understand valencies of elements and radicals.
- Write chemical formulae using valency.
- Differentiate between empirical and molecular formulae.
- Explain the law of conservation of matter in chemical reactions.
Keywords: Chemical symbols, valency, empirical formula, molecular formula, conservation of matter.
Content
1. Chemical Symbols of Elements
- Explanation: Chemical symbols are short forms representing elements on the periodic table (e.g., H for hydrogen, O for oxygen, Na for sodium).
2. Valency
- Definition: Valency is the combining power of an element, indicating how many atoms of hydrogen (or other univalent atoms) an element can combine with or displace.
- Valencies of Elements and Radicals: Elements and radicals have specific valencies (e.g., H has a valency of 1, O has a valency of 2).
- Writing Formulae Using Valencies: The chemical formula of a compound can be written by balancing the valencies of its constituent elements.
3. Empirical and Molecular Formulae
- Empirical Formula: Represents the simplest whole-number ratio of atoms in a compound (e.g., CH₂O for glucose).
- Molecular Formula: Shows the exact number of atoms of each element in a molecule of a compound (e.g., C₆H₁₂O₆ for glucose).
4. Law of Conservation of Matter
- Explanation: This law states that matter is neither created nor destroyed in a chemical reaction, meaning the mass of reactants equals the mass of products.
Evaluation Questions (15 Fill-in-the-Blank Questions with Multiple Choice Options)
- The chemical symbol for oxygen is __________.
- a) O
- b) Ox
- c) Oy
- d) Om
Answer: a) O
- The valency of hydrogen is __________.
- a) 0
- b) 1
- c) 2
- d) 4
Answer: b) 1
- The formula H₂O represents __________.
- a) hydrogen peroxide
- b) hydrogen gas
- c) water
- d) oxygen
Answer: c) water
- __________ is the term for the combining power of an element.
- a) Symbol
- b) Formula
- c) Valency
- d) Mass
Answer: c) Valency
- The empirical formula of glucose is __________.
- a) C₆H₁₂O₆
- b) CH₂O
- c) CO₂
- d) H₂O
Answer: b) CH₂O
- The molecular formula of methane is __________.
- a) CH₄
- b) CO₂
- c) C₆H₆
- d) H₂O
Answer: a) CH₄
- Valency of oxygen is __________.
- a) 1
- b) 2
- c) 4
- d) 8
Answer: b) 2
- A substance that contains only one kind of atom is known as __________.
- a) compound
- b) mixture
- c) element
- d) solution
Answer: c) element
- The chemical symbol for sodium is __________.
- a) S
- b) Na
- c) So
- d) Sm
Answer: b) Na
- The law of conservation of matter states that __________.
- a) energy is created
- b) matter is destroyed
- c) mass is conserved
- d) compounds are formed
Answer: c) mass is conserved
- The valency of chlorine is __________.
- a) 1
- b) 2
- c) 3
- d) 4
Answer: a) 1
- The simplest ratio of atoms in a compound is represented by its __________ formula.
- a) empirical
- b) molecular
- c) structural
- d) ionic
Answer: a) empirical
- The molecule H₂ represents __________.
- a) hydrogen gas
- b) helium
- c) oxygen gas
- d) water
Answer: a) hydrogen gas
- An element with a valency of 3 is likely to form __________ bonds.
- a) one
- b) two
- c) three
- d) four
Answer: c) three
- To balance a chemical equation, you must satisfy the __________.
- a) atomic law
- b) law of gravity
- c) law of conservation of matter
- d) periodic law
Answer: c) law of conservation of matter
Class Activity Discussion (15 FAQs with Answers)
- What is a chemical symbol?
A one- or two-letter abbreviation that represents an element (e.g., O for oxygen). - Why are chemical symbols important?
They provide a universal shorthand to represent elements in chemical equations. - What is valency?
The combining power of an element, showing how many atoms it can combine with or displace. - How is valency used in writing formulas?
By balancing the combining power of elements to create compounds. - What is an empirical formula?
It represents the simplest ratio of atoms in a compound. - What is a molecular formula?
It shows the exact number of atoms of each element in a compound. - What is the difference between empirical and molecular formulae?
The empirical formula shows the simplest ratio, while the molecular formula shows the actual number of atoms. - What does the formula H₂O represent?
The molecular formula of water. - What is the law of conservation of matter?
It states that matter cannot be created or destroyed in a chemical reaction. - Why is the law of conservation of matter important?
It ensures chemical equations are balanced, with equal mass of reactants and products. - How do you identify valencies for different elements?
By using a periodic table or memorizing common valencies for elements and radicals. - What is the symbol for sodium?
Na. - What is the valency of chlorine?
1. - How does conservation of matter apply in chemical equations?
In balanced equations, the number of atoms for each element is the same on both sides. - What happens if a chemical equation isn’t balanced?
It doesn’t correctly represent the conservation of mass.
Evaluation Questions (10 Questions)
- Define chemical symbols.
- What is valency?
- Describe the process of writing chemical formulae using valency.
- What is an empirical formula? Give an example.
- What does the molecular formula of a compound represent?
- Explain the law of conservation of matter.
- Give two examples of elements with valency 1.
- How are molecular formulae different from empirical formulae?
- Why is balancing chemical equations essential?
- What would happen if mass was not conserved in a reaction?
Conclusion
Summarize the importance of chemical symbols, valency, and formulae in chemistry, along with the law of conservation of matter.