Proton or Atomic Number
Q16: Discuss atomic number or proton number in detail?
Atomic Number
What is it?
The atomic number tells us how many protons are in an atom. It is also called the proton number.
Who discovered it?
Henry Moseley discovered the atomic number in 1913.
How is it written?
The atomic number is represented by the symbol Z.
Why is it important?
Each element has a unique number of protons. If an atom had a different number, it would be a different element.
Are atoms neutral?
Yes, because they have the same number of protons (positive) and electrons (negative).
How are elements arranged?
Elements in the periodic table are arranged by their atomic number.
Formula
Atomic Number (Z) = Number of protons = Number of electrons
Examples
| No. | Element | Symbol | Atomic Number |
|---|---|---|---|
| 1 | Hydrogen | H | 1 |
| 2 | Oxygen | O | 8 |
| 3 | Sodium | Na | 11 |
| 4 | Carbon | C | 6 |
| 5 | Helium | He | 2 |
| 6 | Chlorine | Cl | 17 |
Q17: Discuss uniqueness of proton number.
Proton Number: What Makes Elements Unique?
Every element has its own special proton number. This number makes it different from all other elements. It also decides where the element goes in the periodic table.
The periodic table arranges elements by their proton numbers. So, the number of protons helps us find an element's place in the table. Each element is defined by its proton count.
Examples:
- An atom with 6 protons is always carbon.
- An atom with 11 protons is always sodium.
- Every nitrogen atom has 7 protons.
- Every oxygen atom has 8 protons.
You can always recognize an atom by counting its protons!
Q18: Discuss nucleon number or mass number in detail.
Mass Number & Atomic Structure
The mass number of an atom is the total of its protons and neutrons. Electrons are much lighter, so they don’t affect the mass much.
| Element | Symbol | Atomic Number | Mass Number | Protons | Neutrons | Electrons |
|---|---|---|---|---|---|---|
| Hydrogen | H | 1 | 1 | 1 | 0 | 1 |
| Nitrogen | N | 7 | 14 | 7 | 7 | 7 |
| Oxygen | O | 8 | 16 | 8 | 8 | 8 |
| Chlorine | Cl | 17 | 37 | 17 | 20 | 17 |
| Iron | Fe | 26 | 58 | 26 | 32 | 26 |
| Gold | Au | 79 | 197 | 79 | 118 | 79 |
Determining the number of protons and neutrons in an atom Atomic Number of an element is 17 and mass number is 35. How many protons and neutrons are in the nucleus of an atom of this element?
Finding Protons and Neutrons
An element has an atomic number of 17 and a mass number of 35. How many protons and neutrons are in its nucleus?
(1) What is the charge of a particle with 19 protons and 18 electrons?
Understanding Net Charge
Protons have a positive charge (+1). Electrons have a negative charge (-1).
To find the net charge, subtract the electrons from the protons:
19 (protons) - 18 (electrons) = 1
Since the result is +1, the particle has a net positive charge. This means it is a K⁺ ion (potassium ion).
(ii) What is the charge of a particle with 7 protons and 10 electrons?
Understanding Net Charge
Protons have a positive charge (+1), and electrons have a negative charge (-1).
To find the net charge, subtract the electrons from the protons:
7 protons - 10 electrons = -3
Since the result is -3, the particle has a negative charge of -3. This is called a nitride ion (N³⁻).
(iii) What is the difference between the mass number and the atomic mass of an element?
Mass Number vs. Atomic Mass
Mass Number
- The mass number is the total weight of an atom's nucleus.
- It is written in the upper left corner of an element’s symbol.
- It does not consider isotopes; it only focuses on a single atom's weight.
- It is a whole number without decimals.
- The mass number is easy to use for general purposes.
Atomic Mass
- Atomic mass is the average weight of all atoms of an element.
- It is not represented as a symbol.
- It considers isotopes and their natural abundance.
- It includes decimal values because it is a weighted average.
- Atomic mass is useful for precise calculations.
Write the names and symbols for the elements with the following atomic numbers: a. 1 b. 11 c. 19 d. 82 e. 35 f. 47 g. 15 h. 2
Chemistry Basics
Atoms are the building blocks of everything. Each element has a name and a symbol.
Common Elements and Their Symbols
- Hydrogen - H
- Sodium - Na
- Potassium - K
- Lead - Pb
- Bromine - Br
- Silver - Ag
- Phosphorus - P
- Helium - He
What Are Isotopes?
Isotopes are different versions of the same element. They have the same chemical properties but different atomic masses.
How to Calculate Atomic Mass
You can find the relative atomic mass of an element by using the mass and abundance of its isotopes.
3.3 Proton or Atomic Number
Identity of an Element
Proton Number (Atomic Number)
- Symbol: Z
- Refers to the number of protons in the nucleus
- Determines the identity of an element
- Equal to the number of electrons in a neutral atom
Uniqueness of Proton Number
- Each element has a unique proton number
- Determines:
- Element'sproperties
- Position in the periodic table
Examples:
- Carbon: 6 protons
- Sodium: 11 protons
- Nitrogen: 7 protons
- Oxygen: 8 protons
Nucleon Number (Mass Number)
- Total number of protons and neutrons in an atom
- Calculation: No. of neutrons = mass number - atomic number
- Isotopes: Atoms of an element with different numbers of neutrons
Example 3.1: Determining Protons and Neutrons
Given:
Atomic number = 17
Mass number = 35
Solution:
Number of protons = atomic number = 17
Number of neutrons = mass number - atomic number = 35 - 17 = 18
Radioactivity
- Occurs in elements with unbalanced nuclear forces
- Radioactive decay: Process of nucleus decay to become another atom
- Effects on atomic identity:
- Neutron emission: Changes to another isotope of the same element
- Proton emission: Changes to a different element
Examples:
- Carbon-14 decay to Nitrogen-14
- Uranium-238 decay to Lead-206