Atomic Structure Unit Test Version 2

1- The table below gives the atomic mass and the abundance of the two naturally occurring isotopes of chlorine.

Naturally Occuring Isotopes of Chlorine Isotope Atomic Mass of the Isotope Natural Abundance (u) (%) 35Cl 34.97 75.76 37Cl 36.97 24.24

The numerical setup used to calculate the atomic mass of the element chlorine is (34.97 u)(0.7576) + (36.97 u)(0.2424) or (34.97 u)(75.76) + (36.97 u)(24.24) 100 100

2- The energy and the most probable location of an electron in the third shell of an atom is compared to the energy and the most probable location of an electron in the first shell of the same atom as follow: Compared to the energy and location of an electron in the first shell the electron in the third shell has more energy and is farther from the nucleus.

3- The overall charge of an ion that has 12 protons, 10 electrons, and 14 neutrons is 2+ because there are two more protons (12 having positive charge) than the electrons (10 having negative charge). 12+-10- = 2+

4- The subatomic particles found in the nucleus of an atom of Beryllium (like other atoms) are neutrons and protons.

5- According to the wave-mechanical model an orbital is defined as the most probable location of electrons.

42 6- The symbol for an atom containing 20 protons and 22 neutrons is 20Ca because the lower number is the atomic number representing the number of protons and the top number, the mass number, is the sum of protons and neutrons. The number of neutron is calculted by subtracting the atomic number (the number of proton) from the mass number (the sum of protons and neutrons).

7- The electron configuration which represents an atom in the excited state is 2 2 5 2 1s , 2s , 2p , 3s Because there are total 11 electrons and the atom is sodium, the given electronic cofiguration is different than 2,8, 1 (the one given under the symbol of sodium in the periodic table). Furthermore, the given configurations clearly shows that one electron from 2P orbital on the 2nd energy level has jumped to the 3S orbital on the 3rd principal energy level. Hence, proving that this is the excited electronic configuration. 8- The true statement about a proton and an electron is that they have different masses and different charges [ a proton is positively charged and has mass of 1 amu. On the other hand, an electron is negatively charged and has mass of zero (or negligible].

9- As the result of the gold foil experiment it was concluded about the structure of an atom that positively charged nucleus is surrounded by mostly empty space.

10- The atomic mass of Magnesium (like most of the atoms) is the weighted average of the atomic masses of all of the naturally occurring isotopes of Mg.

11- An atom is electrically neutral when the number of protons (positively charged particles) equals the number of electrons (negatively charged particles).

12- The orbital notation which correctly represents the outermost principal energy level of oxygen in the ground state is Because right under the symbol of oxygen in the periodic table the written electronic configuration of oxygen is 2,6, which means the outermost principal energy level of oxygen has 6 electrons.

13- The charge of an electron and the charge of a proton is described as follow: An electron has a charge of -1, and a proton has a charge of +1.

14- The elements arranged in order of increasing atomic mass are Cl, K, Ar.

15-

In the bright-line spectra of three elements and the spectrum of a mixture formed from at least two of the elements mentioned above shows that the mixture contains E and D only because when we project the lines of the mixture spectrum they coincide with the spectral lines of E and D only. 16- The electron configuration which represents the electrons in an atom of Ga in an excited state is 2-8-17-4 because this electronic configuration is different from the electonic configuration given below the symbol of Ga (atomic number 31) in the periodic table. The above given electronic configuration shows that one electon jumped from 3rd principal energy level to 4th principal energy level and that’s why this arrangement is an excited state for Ga.

17- The numbers of protons and neutrons in each of four different atoms are shown in the table below.

Only two atoms, D and E, have the same number of protons but different number of neutrons and therefore, are isotopes of the same element. Atom A with 8 protons is oxygen, atoms D and E with 9 protons are atoms of the same element flourine, and atom G with 10 protons is neon. It is evident that only atom D and E are isotopes of the same elemnt because they have the same number of protons but different number of neutrons.

18- The two notations that represent different isotopes of the same element must have the same number of protons (atomic number). and are isotopes of Beryllium because both the notations have the same atomic number 4 (4 protons in the nucleus). 4 2 19- The atomic mass unit (amu) is defined as exactly 1/12 of the mass of an atom 12 of Carbon-12, which can also be written as 6C

20- The table below gives information about the nucleus of each of the four atoms.

In this table, only two different elements with atomic number (number of protons) 6 and 7 are given. The atom with 6 protons is carbon and the atom with 7 protons is nitrogen. The number of protons is the identity of an atom/element. Therefore, there are only two elements (2 atoms of Carbon and 2 atoms of Nitrogen).