Chapter 12.1/12.2 & Element #2

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The given correct answer "Br" represents the chemical symbol for bromine. Bromine is a halogen element with atomic number 35. Its symbol "Br" is derived from its name. Bromine is a reddish-brown liquid at room temperature and is commonly used in various applications such as flame retardants, water purification, and pharmaceuticals.

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The symbol for gold in the periodic table is Au.

The correct answer is Fe, which is the chemical symbol for iron. Iron is a chemical element with the symbol Fe, derived from the Latin word "ferrum". It is a commonly found metal and has various industrial applications due to its strength, durability, and ability to be magnetized. Iron is an essential element for living organisms and is found in many proteins and enzymes in the body.

The symbol "Ag" stands for the chemical element silver. Silver is a lustrous, white, and precious metal that is known for its high thermal and electrical conductivity. It is commonly used in jewelry, coins, and various industrial applications due to its attractive appearance and excellent properties.

Tungsten is a chemical element with the symbol W, derived from its German name "Wolfram." It is a dense, steel-gray metal known for its high melting point and exceptional strength. Tungsten is commonly used in the production of electrical wires, heating elements, and various alloys due to its excellent heat and corrosion resistance. The symbol "W" represents the element tungsten in the periodic table.

Hg is the chemical symbol for mercury.

The formula for finding density is mass divided by volume. This is because density is defined as the amount of mass per unit volume. By dividing the mass by the volume, we can determine the density of a substance.

Mendeleev is credited with creating the first periodic table. He organized the known elements based on their atomic mass and properties, creating a system that allowed for the prediction of properties for undiscovered elements. Mendeleev's periodic table laid the foundation for our modern understanding of the elements and their relationships, making it the correct answer.

Nonmetals are brittle and not good conductors of heat and electricity. Unlike metals, nonmetals do not have the ability to easily transfer heat or electricity due to their electron configuration. They have high ionization energies and electronegativities, making it difficult for them to lose or gain electrons. This lack of mobility of electrons prevents the flow of electric current. Additionally, nonmetals have a tendency to form covalent bonds rather than metallic bonds, which further restricts the movement of heat and electricity.

A proton is a positively charged particle in an atom's nucleus. It is one of the fundamental particles that make up an atom, along with neutrons and electrons. Protons have a positive charge, which balances the negative charge of electrons in an atom, resulting in a neutral charge overall. The number of protons in an atom determines its atomic number and identifies the element.

Most metals are not brittle; they are known for their malleability and ductility, meaning they can be easily shaped and stretched without breaking. Additionally, metals are good conductors of heat and electricity. Therefore, the characteristic that does not apply to most metals is being brittle.

The correct answer is nucleus. The nucleus is the central part of an atom, containing most of its mass. It is composed of protons and neutrons, which have a much greater mass compared to electrons. The electron cloud, energy level, and shell are all associated with the arrangement of electrons around the nucleus, but they do not contain the majority of the atom's mass.

The properties of an element can be predicted from its location in the periodic table. The periodic table is organized in a way that elements with similar properties are grouped together. This is because elements in the same group have the same number of valence electrons, which determines their chemical reactivity. Additionally, elements in the same period have the same number of electron shells, which affects their atomic radius and ionization energy. Therefore, by knowing an element's location in the periodic table, we can make predictions about its chemical behavior and physical properties.

An atom of uranium has an atomic number of 92, which represents the number of protons in the nucleus. The atomic mass of uranium is 236, which is the sum of the protons and neutrons in the nucleus. Therefore, to find the number of neutrons, we subtract the atomic number from the atomic mass: 236 - 92 = 144. Hence, the correct statement is that an atom of uranium has 144 neutrons.

The given options do not include any examples of physical changes of matter. A physical change refers to a change in the physical properties of a substance, such as shape, size, or state, without altering its chemical composition. However, all the examples provided in the options involve chemical changes. A firefly glowing, wood burning, steam condensing, and a nail rusting all involve chemical reactions where the composition of the substances is altered. Therefore, the correct answer is "None of these."