1. Atomic Number and Mass Number
מספר אטומי ומספר מסה
Atomic Number and Mass Number
מהו מספר אטומי?
The atomic number
is specific for each element.
is the same for all atoms of an element.
is equal to the number of protons in an atom.
appears above the symbol of an element in the periodic table. 11 Na
Atomic Number
Symbol

2. Atomic Number and Protons
דוגמאות
Atomic Number and Protons
Each element has a unique atomic number equal to the
number of protons:
Hydrogen has atomic number 1; every H atom has one proton.
Carbon has atomic number 6; every C atom has six protons.
Copper has atomic number 29; every Cu atom has 29 protons.

3. תרגיל
Learning Check
State the number of protons in each of the following: 1. A nitrogen atom A. 5 protons B. 7 protons C. 14 protons 2. A sulfur atom A. 32 protons B. 16 protons C. 6 protons 3. A barium atom A. 137 protons B. 81 protons C. 56 protons

4. פתרון
Solution
State the number of protons in each of the following: 1. A nitrogen atom B. 7 protons 2. A sulfur atom B. 16 protons 3. A barium atom C. 56 protons

5. Number of Electrons in an Atom
מספר האלקטרונים
Number of Electrons in an Atom
All atoms of an element are electrically neutral; they
have
a net charge of zero.
an equal number of protons and electrons.
Number of protons = Number of electrons
= atomic number
Example:
Aluminum atoms have 13 protons and 13 electrons; the
net charge is zero.

6. מספר מסה
The mass number represents the number of subatomic particles in the nucleus, which is equal to the sum of the number of protons + number of neutrons. Since protons and neutrons account for the majority of mass in an atom, we call this the mass number.

7. בטבלה המחזורית היסודות מסודרים בסדר של מס' אטומי עולהH He Be B
Mass number : 7
4 neutron
Mass number : 12
6 neutron

8. Composition of some atoms of different elements
הרכב האטומים (מס' פרוטונים, ניוטרונים ואלקטרונים) של יסודות שונים
Composition of some atoms of different elements
Number of electrons
Number of neutrons
Number of protons
Mass number
Atomic number
Symbol
Element 1 H
Hydrogen 7 14 N
Nitrogen 17 20 37 Cl
Clorine 26 31 57 I
Iron 79
118
197 AU
Gold

9. תרגיל
Learning Check
An atom of zinc has a mass number of How many protons are in a zinc atom? A. 30 B. 35 C How many neutrons are in a zinc atom? 3. What is the mass number of a zinc atom that has 37 neutrons? A. 37 B. 65 C. 67

10. פתרון
Solution
An atom of zinc has a mass number of How many protons are in a zinc atom? A. 30 (atomic number is 30) 2. How many neutrons are in a zinc atom? 3. What is the mass number of a zinc atom that has 37 neutrons?

11. תרגיל
Learning Check
An atom has 14 protons and 20 neutrons. 1. What is its atomic number? A. 14 B. 20 C What is its mass number? 3. What is this element? A. Si B. Ca C. Ar

12. פתרון
Solution
An atom has 14 protons and 20 neutrons. 1. What is its atomic number? A What is its mass number? C What is this element? A. Si (atomic number 14)