What is the simplest way of explaining what atoms, elements, compounds and mixtures are?
Atoms are the smallest bits of ordinary matter and are made from particles called protons (which carry a positive electrical charge), neutrons (which carry no electrical charge) and electrons (which carry a negative electrical charge). The protons and neutrons cluster together in the central part of the atom, called the nucleus, and the electrons 'orbit' the nucleus. A particular atom will have the same number of protons and electrons and most atoms have at least as many neutrons as protons.
An element is a substance that is made entirely from one type of atom. For example, the element hydrogen is made from atoms containing just one proton and one electron. If you had very, very good eyes and could look at the atoms in a sample of hydrogen, you would notice that most of the atoms have no neutrons, some of them have one neutron and a few of them have two neutrons. These different versions of hydrogen are called isotopes. All isotopes of a particular element have the same number of protons, but can have different numbers of neutrons. If you change the number of protons an atom has, you change the type of element it is. If you change the number of neutrons an atom has, you make an isotope of that element. All known elements are arranged on a chart called the Periodic Table of Elements.
A compound is a substance made from two or more different elements that have been chemically joined. Some examples of compounds are water (H2O), table salt (NaCl), table sugar (C12H22O11) and chalk (CaCO3).
A mixture is a substance made by combining two or more different materials in such a way that no chemical reaction occurs. A mixture can usually be separated back into its original components. Some examples of mixtures are a tossed salad, salt water and a mixed bag of M&M's candy.
Author:
Steve Gagnon, Science Education Specialist (Other answers by Steve Gagnon)
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Which of the following defines the identity of an element?
Possible Answers:
Number of electron shells
Correct answer:
Number of protons
Explanation:
The identity of an element is determined by the number of protons. One cannot alter the number of protons without altering the identity of the element. By adding a proton, the atomic number increases by one and the element identity changes.
Number of neutrons can be altered to create isotopes. Number of electrons can be altered to create ions.
What element could contain seven protons, eight neutrons, and seven electrons?
Possible Answers:
Depending on isotope and ionization, any of these could have the given configuration
Explanation:
An element is defined by its number of protons. Varying the number of neutrons will change the isotope of an element and varying the number of electrons will create an ion, but changing the number of protons changes the identity of the element itself. Nitrogen has atomic number seven, and is the only element that can have seven protons. The given configuration is for an isotope of nitrogen. Since there are eight neutrons, this atom would be for nitrogen-15.
Which of the following molecules consists of only one element?
Possible Answers:
Correct answer:
Explanation:
Elements are shown on the periodic table. Compounds are made when one or more element is combined to form a molecule. The smallest unit of an element is an atom, while the smallest unit of a compound is a molecule.
Of the given answer choices, only satisfies the question criteria. This is the formula for a molecule of bromine gas, made of two bromine atoms.
is the formula for hydrochloric acid and is the formula for water. Both of these compounds are composed of molecules, but hydrochloric acids contains both hydrogen and chlorine atoms, and water contains both hydrogen and oxygen.
Is it possible to form a compound from only one element?
Possible Answers:
Yes; benzene rings contain only carbon
Yes; water is a compound that consists of only one element
Yes; compounds and elements are synonyms
Yes; diatomic gases are compounds that consist of only one element
No; a compound must contain multiple elements
Correct answer:
Yes; diatomic gases are compounds that consist of only one element
Explanation:
Elements are defined by the number of protons in a given atom, and the atom is the smallest unit of an element. In contrast, a compound is defined by the identity and organization of multiple atoms, with the smallest unit of a compound being a molecule.
Some compounds do contain only one element, such as diatomic gases or graphite. Benzene rings are composed of carbon and hydrogen, while water molecules contain hydrogen and oxygen.
Which of the following atomic properties, if known, will reveal the identity of the element?
Possible Answers:
More than one of these answers could allow us to identify the given atom
Correct answer:
The number of protons
Explanation:
There are two properties that can be used to identify an element: the atomic number or the number of protons in an atom.
The number of neutrons and number of electrons are frequently equal to the number of protons, but can vary depending on the atom in question. Different ions and isotopes will alter the number of neutrons and electrons, making these properties unreliable identifiers. Similarly, atomic mass will vary with the number of neutrons present and cannot be used to establish atomic identity.
Which of the following phase labels are used for all diatomic elements?
Possible Answers:
Explanation:
Diatomic elements are commonly referred to as diatomic gases because whenever they are by themselves, they bond to themselves (that is where the "2" subscript comes from). Anytime diatomic elements have that "2" subscript, they have the gas (g) phase label. For example,
What is the chemical symbol for potassium?
Possible Answers:
Explanation:
The symbol for potassium comes from the latin word for potassium, kalium. That is why the chemical symbol for potassium is
Which element also goes by its latin name, ferrum?
Possible Answers:
Explanation:
The word for iron in latin is ferrum, thus, the chemical symbol for iron is
Which element has 42 protons?
Possible Answers:
Correct answer:
Molybdenum
Explanation:
Remember, the number of protons is equal to the atomic number of the element. Look at the periodic table and find the element with atomic number 42, it corresponds to molybdenum.
Which element has 17 electrons?
Possible Answers:
Explanation:
Since atoms are neutral, the number of electrons must equal the number of protons (to balance the negative and positive charges). Thus the element with 17 electrons also has 17 protons. The number of protons is equal to the atomic number of the element. Use the periodic table to find the element with atomic number 17, chlorine. Note that ions are not neutral, thus they have unequal numbers of protons and electrons. Also, isotopes of the same element contain differing numbers of neutrons, which also affects the weight of the isotope.
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