1.8 Nearly all of the mass is located in the nucleus, because this is the portion of the atom where the proton(s) and the neutron(s), the heaviest constituent particles of the atom, are located.
1.9 Electrons are much lighter (about 10 000 times) than both protons and neutrons. Therefore, their contribution to the overall mass of an atom can be neglected for all but the most precise of measurements.
1.10 The atomic number is equal to the number of protons in the nucleus of the atom, and the mass number is the sum of the neutrons and the protons.
1.11 Isotopes are atoms of an element having identical numbers of protons (and therefore the same atomic numbers) but differing numbers of neutrons (and therefore different mass numbers). Their chemical behaviour is similar because the chemistry of an atom is determined primarily by its atomic number. For example, the isotopes protium, deuterium and tritium all undergo reactions typical of hydrogen, despite the fact they have different mass numbers.
1.12 (a) A is the mass number (number of protons + number of neutrons).
(b) Z is the atomic number (number of protons).
1.13 (a)
(b)
(c)
(d)
1.14 (a) Cl
(b) S
(c) Fe
(d) Ag
(e) Na
(f) P
(g) I
(h) Cu
(i) Hg
(j) Ca
1.15 (a) lithium
(b) gold
(c) uranium
(d) arsenic
(e) cobalt
(f) bromine
(g) platinum
(h) boron
(i) neon
(j) beryllium
1.16 Mendeleev constructed his periodic table by arranging the elements in order of increasing atomic weight and grouping the elements by their recurring properties. The modern periodic table is arranged in order of increasing number of protons (increasing atomic number).
1.17 False. A period in the periodic table is a horizontal row of elements. It is the elements in a group, one of the vertical columns of the periodic table, that behave chemically similarly.
1.18 Not all of the elements had yet been discovered; therefore Mendeleev left spaces for the ones that he predicted would eventually be discovered because he grouped elements with similar chemical properties together.
1.19 The atomic number — the number of protons in the nucleus (and the number of electrons in the neutral atom) — is related to the chemistry of an element. The periodic table is based on atomic numbers. The mass numbers, which vary with the number of neutrons in the atom, do not affect the chemistry of the elements as much as the number of protons.
1.20 Strontium and calcium are in the same group of the periodic table, so they are expected to have similar chemical properties. Strontium should therefore form compounds that are similar to those of calcium, including the types of compounds found in bone.
1.21 Palladium and platinum are in the same group of the periodic table as nickel (group 10), so they might well be expected to occur together in nature because of their similar chemical properties and tendencies to form similar compounds.
1.22 Cadmium is in the same periodic table group as zinc, but silver is not. Therefore cadmium is expected to have properties similar to those of zinc, and should therefore be found together with it in nature.
1.23 There is simply no space in the periodic table for another element having an atomic number less than 92. All the elements from atomic number 1 (hydrogen) to atomic number 92 (uranium) have been discovered and accounted for. The only new elements that will be discovered are those with high atomic numbers. At present, the elements up to an atomic number of 118 are known. Any new elements will have atomic numbers greater than this.