Isotopes and Atomic Mass איזוטופים ומסה אטומית Isotopes and Atomic Mass מהם איזוטופים? Isotopes are atoms of the same element that have different mass numbers. have the same number of protons but different numbers of neutrons. can be distinguished by atomic symbols. כיצד מסמנים אותם?

איזוטופים של מגנזיום

איזוטופים של מגנזיום 26Mg 12 25Mg 24Mg Atomic symbol Number of protons Number of electrons 26 25 24 Mass number 11.2% 10.1% 78.7% % abundance 14 13 Number of neutrons

Isotopes and Mass and Atomic Symbols סמל אטומי של איזוטופים Isotopes and Mass and Atomic Symbols Since each isotope of an element has a different number of neutrons, each isotope’s mass number will be different. We write these as atomic symbols: Mass numbers are in the upper left corner. Atomic numbers are in the lower left corner. Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number atomic number 23 Na 11

O P Zn דוגמאות לסמל אטומיים 16 65 For an atom, the atomic symbol gives the number of protons (p+), neutrons (n), and electrons (e–). 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n 8 e– 15 e– 30 e– 16 8 O 31 15 P 65 30 Zn

Learning Check C C C תרגיל 1 Naturally occurring carbon consists of three isotopes: C-12, C-13, and C-14. State the number of protons, neutrons, and electrons in each of the following. Protons ______ ______ ______ Neutrons ______ ______ ______ Electrons ______ ______ ______ 12 6 C 13 6 C 14 6 C

Solution C C C פתרון תרגיל 1 Protons 6 p+ 6 p+ 6 p+ Neutrons 6 n 7 n 8 n Electrons 6 e– 6 e– 6 e– 12 6 C 13 6 C 14 6 C

תרגיל 2 Learning Check Write the nuclear symbols for atoms with the following subatomic particles: 1. 9 p+, 10 n, 9 e– ___________ 2. 17p+, 20 n, 17 e– ___________ 3. 47p+, 60 n, 47 e– ___________

Solution F Cl Ag פתרון תרגיל 2 Write the nuclear symbols for atoms with the following subatomic particles: 1. 9 p+, 10 n, 9 e– 2. 17p+, 20 n, 17 e– 3. 47p+, 60 n, 47 e– 19 9 F 37 17 Cl 107 47 Ag

Learning Check X X Z Z Z Z תרגיל 3 1. Which of the following pairs are isotopes of the same element? 2. In which of the following pairs do both atoms have 8 neutrons? A. B. C. 12 X 15 X 6 7 12 Z 14 Z 6 6 15 Z 16 Z 7 8

Solution Z Z פתרון תרגיל 3 1. Which of the following pairs are isotopes of the same element? B. Same number of protons, different number of neutrons. 2. In which of the following pairs do both atoms have 8 neutrons? 12 Z 14 Z 6 6

האיזוטופים של מגנזיום בעלי שכיחות שונה בטבע

השכיחות של האיזוטופים של גופרית A sample of naturally occurring sulfur contains several isotopes with the following abundances: Isotope % Abundance 95.02 0.75 4.21 0.02 32 16 S 33 16 S 34 16 S 36 16 S

מסה אטומית Na 22.99 The atomic mass of an element is listed below the symbol of each element on the periodic table. gives the mass of an “average” atom of each element compared to C-12. is not the same as the mass number. is calculated using a weighted average. Na 22.99

מסה אטומית של כלור The atomic mass of chlorine is based on all naturally occurring Cl isotopes. not a whole number. the weighted average of the Cl-35 and Cl-37 isotopes.

חישוב המסה האטומית של מגנזיום To calculate the atomic mass of an element, we need to know the percent abundance of each isotope and its mass.

מסה אטומית של מגנזיום The atomic mass of Mg is based on all naturally occurring Mg isotopes. not a whole number. the weighted average of the Mg-24, Mg-25, and Mg-26 isotopes.

חישוב המסה האטומית של מגנזיום To calculate the atomic mass of Mg, we use a weighted average because the atomic mass is calculated from the percent abundance of each isotope and its mass.

מסה אטומית של יסודות שונים Most elements have two or more isotopes that contribute to the atomic mass of that element.

תרגיל 4 Learning Check Using the periodic table, give the atomic mass for each of the following elements. 1. calcium __________ 2. aluminum __________ 3. lead __________ 4. barium __________ 5. iron __________

פתרון תרגיל 4 Solution Using the periodic table, give the atomic mass for each of the following elements. 1. calcium 40.08 amu 2. aluminum 26.98 amu 3. lead 207.2 amu 4. barium 137.3 amu 5. iron 55.85 amu

תרגיל 5 Learning Check The atomic mass of chlorine is 35.45 amu. Based on this information, which of the following isotopes of Cl is present in the largest amount? A. Cl-35 B. Cl-37

פתרון תרגיל 5 Solution The atomic mass of chlorine is 35.45 amu. Based on this information, which of the following isotopes of Cl is present in the largest amount? Solution: A. Cl-35 Since 35.45 amu is very close to the mass number of 35, the isotope Cl-35 is the most prevalent isotope in a naturally occurring sample of chlorine atoms.