Atomic Structure Chemistry Quiz

The mass number of an atom is calculated by adding the number of protons and neutrons together. In this case, the atom has 17 protons and 18 neutrons. Therefore, the mass number is 17 (protons) + 18 (neutrons) = 35. This total reflects the overall mass of the atom, as protons and neutrons contribute significantly to the atomic mass, while electrons have a negligible effect.

An atom maintains no overall charge because it contains equal numbers of protons and electrons. Protons, which are positively charged, balance the negatively charged electrons. When these charges are equal, they cancel each other out, resulting in a neutral atom. Neutrons, which have no charge, do not affect the overall charge of the atom. Therefore, the balance between protons and electrons is crucial for an atom to remain electrically neutral.

The electron configuration 2, 8, 7 indicates the distribution of electrons in the electron shells of an atom. The first shell holds 2 electrons, the second shell holds 8 electrons, and the third shell holds 7 electrons. Therefore, in this configuration, the third shell contains 7 electrons, which is directly stated by the last number in the sequence. This reflects the atom's ability to accommodate electrons in its outermost shell, influencing its chemical properties and reactivity.

Atoms with the same number of protons but different numbers of neutrons are known as isotopes. In this case, both atoms have 8 protons, classifying them as the same element, but the variation in neutrons (8 in one atom and 10 in the other) leads to different isotopes of that element. This difference in neutron count affects the atomic mass but not the chemical properties, defining them as isotopes of the same element.

A substance formed from two or more types of atoms chemically bonded together is known as a compound. Compounds have distinct properties that differ from the individual elements that compose them. The atoms in a compound are held together by chemical bonds, which can be ionic or covalent, depending on how the atoms interact. This definition distinguishes compounds from mixtures, where the components retain their individual properties and are not chemically bonded.

Crystallisation is the most appropriate technique to separate salt from water because it involves the evaporation of water, allowing the salt to form solid crystals as the solution becomes supersaturated. This method effectively separates the soluble solid (salt) from the liquid (water) by taking advantage of the differences in solubility and the physical properties of the substances involved. It is particularly useful when the goal is to recover the salt in a pure crystalline form.

An ion is indeed formed when an atom either loses or gains electrons, leading to an imbalance between the number of protons and electrons. When an atom loses electrons, it becomes positively charged, known as a cation. Conversely, when it gains electrons, it acquires a negative charge, becoming an anion. This process is fundamental in chemistry, as ions play crucial roles in various chemical reactions, electrical conductivity, and the formation of compounds. Thus, the statement accurately describes the nature of ions.

A mixture consists of two or more substances that are physically combined but not chemically bonded. This means that the individual components retain their own properties and can be separated by physical means, such as filtration or evaporation. Unlike compounds, where elements are chemically bonded in fixed ratios, mixtures can vary in composition and do not have a uniform structure. Therefore, the correct statement highlights the nature of mixtures as combinations of substances without chemical bonds.

The second and third electron shells of an atom can hold a maximum of 8 electrons each due to the distribution of electrons in atomic orbitals. The second shell (n=2) can accommodate up to 8 electrons (2 in the s orbital and 6 in the p orbitals). Similarly, the third shell (n=3) can also hold 8 electrons in its s and p orbitals, despite having d orbitals available, which are filled after the p orbitals. This follows the octet rule, which states that atoms are most stable with 8 electrons in their outer shell.