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

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.

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

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

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.

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.

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

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

תרגיל Learning Check An atom of zinc has a mass number of 65. 1. How many protons are in a zinc atom? A. 30 B. 35 C. 65 2. 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

פתרון Solution An atom of zinc has a mass number of 65. 1. 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?

תרגיל Learning Check An atom has 14 protons and 20 neutrons. 1. What is its atomic number? A. 14 B. 20 C. 34 2. What is its mass number? 3. What is this element? A. Si B. Ca C. Ar

פתרון Solution An atom has 14 protons and 20 neutrons. 1. What is its atomic number? A. 14 2. What is its mass number? C. 34 3. What is this element? A. Si (atomic number 14)