Question

1. what 2 pieces of info do you need to calculate the average atomic mass of an element? 1. 2. 16. most atoms naturally have more than protons. a. electrons b. neutrons c. positive charge d. electron clouds 17. what does the number represent in calcium - 42? a. number of electrons b. number of protons c. number of neutrons d. mass number 18. what does the number in ca^{+2} represent? a. number of neutrons lost b. number of neutrons gained c. number of electrons lost d. number of protons gained 19. the mass of an atom with 10 protons, 11 neutrons and 12 electrons is? a. 21 b. 22 c. 23 d. - 2 20. what are the numbers of protons, neutrons and electrons in _{14}^{29}si? a. 15 protons, 14 neutrons, 15 electrons b. 14 protons, 15 neutrons, 14 electrons c. 14 protons, 15 neutrons, 15 electrons d. 15 protons, 14 neutrons, 14 electrons

Explanation:

• Question 16: Atoms are neutral (protons = electrons). Neutrons are often more than protons (e.g., in many stable isotopes). Positive charge is due to protons. Electron - clouds are regions, not particles.
• Question 17: In the notation like Calcium - 42 (or \(^{42}\text{Ca}\)), the number represents the mass number (\(A=\text{protons}+\text{neutrons}\)).
• Question 18: For \(Ca^{+ 2}\), the \(+2\) charge means it has lost 2 electrons (protons \(>\) electrons by 2). Neutrons are not involved in ion - charge formation (except in some nuclear reactions, but not in simple ion - formation). Protons are in the nucleus and not lost/gained easily in chemical ion - formation.
• Question 19: Mass of an atom is given by \(A=\text{protons}+\text{neutrons}\). Electrons have negligible mass. So \(A = 10+11=21\).
• Question 20: For \(\ce{^{29}_{14}Si}\), the atomic number \(Z = 14\) (number of protons). In a neutral atom, number of electrons = number of protons. Mass number \(A = 29\), so number of neutrons \(N=A - Z=29 - 14=15\).

Answer:

1. B. Neutrons
2. D. Mass number
3. C. Number of electrons lost
4. A. 21
5. B. 14 protons, 15 neutrons, 14 electrons