This means a neutral oxygen atom has eight protons and eight electrons. The element Actium Ac has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom. Table 2. Neutrons affect the mass of an atom and play a role in the stability of atoms.
Unlike protons, the numbers of neutrons in elements varies. For example, most hydrogen atoms have no neutrons, but a few have one neutron, and some rare hydrogen atoms have two neutrons.
Most helium atoms have two neutrons, but some have three neutrons. The periodic table Fig. In Fig. In Figure 2. The periodic table has three prominent features. First, the periodic table is arranged in horizontal rows, which are called periods. There are seven periods. In Period 1 there are two elements, hydrogen H and helium He. The second and third periods both contain eight elements, the fourth and fifth periods contain 18 elements, and the sixth and seventh periods contain 32 elements.
Second, all of the elements are listed sequentially according to their atomic numbers. For example, in Figure 2. Third, the periodic table is arranged in columns of elements that react similarly. These columns are called groups. The group number is found at the top of the column. Groups 1—12 contain only metals, Groups 13—16 contain both metals and nonmetals, and Groups 17 and 18 contain only nonmetals.
One exception is hydrogen. Although technically a nonmetal, hydrogen has properties of both metals and nonmetals and is often placed in Group 1. The two long rows that are at the bottom of the periodic table are exceptions. The elements in each of these rows behave similarly, so are considered groups.
These two groups are arranged in rows rather than columns. Metals are elements that conduct heat and electricity. Metals are usually malleable , they can be bent or molded without breaking, and lustrous , or shiny. Most metals are silvery in color Fig. Most metals are solid at room temperature. One exception is mercury Hg , which is a liquid at room temperature Fig. The elements in Group 1, including lithium Li , sodium Na, Fig.
These metallic Group 1 elements have similar reactive properties. Related questions Question f13ae. Question bb7b1. Question Question fd74b. Question f13b2. How do I find the molar mass of an element? What is an element? A compound is pure as well because it is made up of only one type of molecule. Breaking down a compound further would only lead to the individual atoms or individual elements that comprise that compound.
Particular physical and chemical properties are associated with pure substances. Breaking down those pure substances would only lead to components that have entirely different physical and chemical properties from the pure substance itself.
In chemistry, homogeneous means that a substance has the same appearance and uniform composition throughout. Put simply, a slab comprised of the element silver has only silver atoms throughout. Additionally, the entire slab exhibits both physical and chemical properties of the element silver.
But a rusting slab of tin is not considered homogeneous. By the same token, the compound water is homogeneous when it is pure. If the water is contaminated, it is not homogeneous anymore, but heterogeneous. So a pure element and a pure compound are both homogeneous because they are untainted and retain all their properties consistently. Mariecor Agravante earned a Bachelor of Science in biology from Gonzaga University and has completed graduate work in Organizational Leadership.
Two atoms of the same element can be different if their electrons are in different states. If one copper atom has an electron in an excited state and another copper atom has all of its electrons in the ground state, then the two atoms are different.
The excited copper atom will emit a bit of light when the electron relaxes back down to the ground state, and the copper atom already in the ground state will not. Since the states of the electrons in an atom are what determine the nature of the chemical bonding that the atom experiences, two atoms of the same element can react differently if they are in different states. For instance, a neutral sodium atom say, from a chunk of sodium metal reacts with water much more violently than an ionized sodium atom say, from a bit of salt.
Chemists know this very well. It's not enough to say what atoms are involved if you want to fully describe and predict a reaction. Even if left alone, an atom often does not come with an equal number of protons and electrons. But what if two atoms of the same element both have their electrons in the same states. Then are they identical?
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