1. An isotope of chromium is represented by Cry. Which statement about an atom of
this isotope of chromium is correct?
A It contains 24 electrons.
B It contains 24 neutrons.
C It contains 28 protons.
D It contains 52 neutrons.
Answers
Answer:
Isotopes
As stated earlier, not all atoms of a given element are identical. Specifically, the number of neutrons in the nucleus can vary for many elements. As an example, naturally occurring carbon exists in three forms, which are illustrated in the figure below.
Figure 2.1.2: Nuclei of the three isotopes of carbon. Almost \(99\%\) of naturally occurring carbon is carbon-12, whose nucleus consists of six protons and six neutrons. Carbon-13 and carbon-14, with seven or eight neutrons, respectively, have a much lower nuclei abundance.
Each carbon atom has the same number of protons (6), which is equal to its atomic number. Each carbon atom also contains six electrons, allowing the atom to remain electrically neutral. However, the number of neutrons varies from six to eight. Isotopes are atoms that have the same atomic number but different mass numbers due to a change in the number of neutrons. The three isotopes of carbon can be referred to as carbon-12 \(\left( \ce{^{12}_6C} \right)\), carbon-13 \(\left( \ce{^{13}_6C} \right)\), and carbon-14 \(\left( \ce{^{14}_6C} \right)\). Naturally occurring samples of most elements are mixtures of isotopes. Carbon has only three natural isotopes, but some heavier elements have many more. Tin has ten stable isotopes, which is the most of any known element. The nucleus of a given carbon atom will be one of the three possible isotopes discussed above.
While the presence of isotopes affects the mass of an atom, it does not affect its chemical reactivity. Chemical behavior is governed by the number of electrons and the number of protons. Carbon-13 behaves chemically in exactly the same way as the more plentiful carbon-12.
Size of Atoms
The graphite in your pencil is composed of the element carbon, a nonmetal. Imagine taking a small piece of carbon and grinding it until it is a fine dust. Each speck of carbon would still have all of the physical and chemical properties of carbon. Now imagine that you could somehow keep dividing the speck of carbon into smaller and smaller pieces. Eventually, you would reach a point where your carbon sample is as small as it could possibly be. This final particle is called an atom.
Atoms, as you probably know, are extremely small. In fact, the graphite in an ordinary pencil contains about \(5 \times 10^{20}\) atoms of carbon. This is an almost incomprehensibly large number. The population of the entire Earth is about \(7 \times 10^9\) people, meaning that there are about \(7 \times 10^{10}\) times as many carbon atoms in your pencil as there are people on Earth! For this to be true, atoms must be extremely small.
Explanation: