A)    Atomic mass

B)    Number of neutrons

C)    Number of valence electrons

D)    Atomic number

Correct Answer: Option D - Atomic number

The atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element. In an atom of neutral charge, atomic number is equal to the number of electrons.

Incorrect Options

Valence electrons are the outermost electrons of an atom, which are important in determining how the atom reacts chemically with other atoms. Atoms with a complete shell of valence electrons (corresponding to an electron configuration s²p⁶) tend to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive because the extra electrons are easily removed to form positive ions. Atoms with one or two valence electrons less than a closed shell are also highly reactive because of a tendency either to gain the missing electrons and form negative ions, or to share electrons and form covalent bonds.

The atomic weight is basically a measurement of the total number of particles in an atom's nucleus. The atomic weight is actually a weighted average of all of the naturally occurring isotopes of an element relative to the mass of carbon-12.

Number of Neutrons = Atomic Mass - Atomic Number

A)    The sum of the masses of 1 electron and 1 proton

B)    Mass of 2 electrons

C)    Mass of 2 neutrons

D)    The sum of the masses of 1 neutron and 1 electron

Correct Answer: Option B - Mass of 2 electrons

• Mass of proton: 1.6726 x 10^-27 kg
• Mass of neutron: 1.6749 x 10^-27 kg
• Mass of electron: 0.00091x10^-27 kg

Using the above information, when we add the mass of 2 electrons it is the lowest of all the options; hence, the answer is option B

A)    A negatively charged electron cloud surrounding a positively charged nucleus

B)    A positively charged electron cloud surrounding a positively charged nucleus

C)    A positively charged electron cloud surrounding a negatively charged nucleus

D)    A negatively charged electron cloud surrounding a negatively charged nucleus

Correct Answer: Option A - A negatively charged electron cloud surrounding a positively charged nucleus

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral; otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.

A)    Electron and neutron

B)    Electron and positron

C)    Proton and neutron

D)    Proton and electron

Correct Answer: Option C - Proton and neutron

• Mass of proton: 1.6726 x 10^-27 kg
• Mass of neutron: 1.6749 x 10^-27 kg
• Mass of electron: 0.00091x10^-27 kg

The unified atomic mass unit (u), or dalton (Da) or, sometimes, universal mass unit, is a unit of mass used to express atomic and molecular masses. It is the approximate mass of a hydrogen atom, a proton, or a neutron.

The precise definition is that it is one twelfth of the mass of an isolated atom of carbon-12 (¹²C) at rest and in its ground state.

1 u = 1/NA gram = 1/ (1000 NA) kg   (where NA is Avogadro's number)

1 u = 1.660538782(83) × 10^-27 kg

A)    Atoms travel in defined circles

B)    Atoms are most likely found in an excited state

C)    Atoms have a positive charge

D)    Atoms are located in orbitals outside the nucleus

Correct Answer: Option D - Atoms are located in orbitals outside the nucleus

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons, in an atom.[1] This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. These functions may serve as three-dimensional graph of an electron's likely location. The term may thus refer directly to the physical region defined by the function where the electron is likely to be. Specifically, atomic orbitals are the possible quantum states of an individual electron in the collection of electrons around a single atom, as described by the orbital function. The wave mechanical model, influenced by the Heisenberg uncertainty principle, says that electrons do not orbit in fixed orbits. In fact, it's impossible to know both the position and momentum of a particle like an electron. Instead the wave mechanical model uses the Schroedinger equation to predict the probabilities of where the electron may be positioned at any given time (without saying with any certainty where the electron actually is).

According to Heisenberg's uncertainty principle, it is impossible to describe the exact position of an electron at a given moment in terms of position; we can speak of most probable regions where the probability of finding an electron in the space around the nucleus of an atom is high. The electron does not always remain at a fixed distance from a nucleus. It keeps moving in the whole space around the nucleus but tends to remain most of the time within a small volume around the nucleus, where the probability of locating the electron is maximum.

A)    A compound

B)    An element

C)    A solution

D)    An isomer

Correct Answer: Option B - An element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.

Incorrect Options

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions and that have a unique and defined chemical structure. Chemical compounds consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by chemical bonds. Chemical compounds can be compound molecules held together by covalent bonds, salts held together by ionic bonds, metallic compounds held together by metallic bonds, or complexes held together by coordinate covalent bonds. Substances such as pure chemical elements and elemental molecules consisting of multiple atoms of a single element (such as H₂, S₈, etc.) are not considered chemical compounds.

A solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. Gases may dissolve in liquids, for example, carbon dioxide or oxygen in water. Liquids may dissolve in other liquids. Gases can combine with other gases to form mixtures, rather than solutions.

Isomers are compounds with the same molecular formula but different structural formula. Isomers do not necessarily share similar properties unless they also have the same functional groups.

A)    In the third shell, an electron has more energy and is closer to the nucleus.

B)    In the third shell, an electron has less energy and is closer to the nucleus.

C)    In the third shell, an electron has less energy and is farther from the nucleus.

D)    In the third shell, an electron has more energy and is farther from the nucleus.

Correct Answer: Option D - In the third shell, an electron has more energy and is farther from the nucleus.

Electrons in an atom are arranged in shells around the nucleus. Shells are orbits around the nucleus followed by electrons. Because each shell can contain only a fixed number of electrons, each shell is associated with a particular range of electron energy, and thus each shell must fill completely before electrons can be added to an outer shell.

The electrons in the outermost shell determine the chemical properties of the atom; and these electrons known as valence electrons, have the highest energy to react with other atoms due to their distance from the nucleus. Atoms with a complete shell of valence electrons (corresponding to an electron configuration s²p⁶) tend to be chemically inert. Atoms with one or two valence electrons more than a closed shell are highly reactive.

A)    Nickel

B)    Iodine

C)    Mercury

D)    Sulfur

Correct Answer: Option A - Nickel

Nickel is silvery-white, malleable and ductile metal. It is one of the elements of the iron group and it takes on a high polish. It is a solid and a fairly good conductor of heat and electricity at STP; due to its characteristic of being bivalent.

Incorrect Options

Iodine is a non-metallic, dark-gray, lustrous, solid element, generally available in powdered form. It is the most electropositive and least reactive halogen. It is not a good conductor of electricity.

Mercury also called as quicksilver is a silvery-white liquid metal, and a poor conductor of heat compared to other metals; but it is a fair conductor of electricity.

Sulfur is a multivalent non-metal, abundant, tasteless and odorless. In its native form sulfur is a yellow crystalline solid. In nature it occurs as the pure element or as sulfide and sulfate minerals. It is not a good conductor of electricity.

A)    Bromine

B)    Fluorine

C)    Chlorine

D)    Iodine

Correct Answer: Option B - Fluorine

Atoms can attract additional electrons if there is room for them in the valence energy level. When an extra electron moves into the valence shell, it can feel the attraction exerted by the effective nuclear charge. Because the effective nuclear charge is largest for the elements on the right side of the periodic table, those atoms provide the greatest attraction for electrons and have the greatest tendency to gain electrons. Thus the tendency of atoms to gain electrons increases as we go from left to right across the periodic table. At least it increases until we get to the inert gases. There it drops off to zero because there is no room for additional electrons in the valence energy level. A new electron would have to start a new energy level, but there would not be an additional proton in the nucleus to provide any effective nuclear charge.

As we look at elements going down the periodic table, the effective nuclear charge remains the same, so the increase in the number of energy levels is the important factor. The tendency of atoms to gain electrons decreases as we go down the periodic table. The reason for this is simply that with the larger atoms the added electron is not as close to the nucleus and therefore the attractive force exerted by the effective nuclear charge is not as powerful as it is in the smaller atoms.

A)    Number of protons equals the number of electrons

B)    Number of protons equals the number of neutrons

C)    Ratio of the number of neutrons to the number of electrons is 1:1

D)    Ratio of the number of neutrons to the number of protons is 2:1

Correct Answer: Option A - Number of protons equals the number of electrons

The atom is a basic unit of matter consisting of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutron). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral; otherwise it has a positive or negative charge and is an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.