The nonmetals in Group 17 are all diatomic two atoms in their elemental form and have similar reactive properties. There are other organizational features of the periodic table. Most periods have the first element of the period in Group 1 and the last element in Group An exception is the first period. Sometimes hydrogen H is placed in Group 17, above fluorine F , because it has similar properties to the nonmetals in that group; for example, in its elemental state hydrogen exists as a diatomic gas, H2.
Sometimes hydrogen is placed in both Groups 1 and Groups of elements have similar properties. The properties of some groups are so unique or important that the groups are referred to by special names. The elements in this group are called the noble gases. Noble gases seldom react with other elements. Noble gases have many uses, for example, they are used in neon signs Fig 2.
Group 1 is often referred to as the alkali metals, Group 2 as the alkaline earth metals, and Group 17 as the halogens. The two groups that are pulled out on the bottom of the periodic table in rows are called the lanthanide rare earth series top row and the actinide series bottom row.
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Atoms, Molecules, and Compounds. NGSS Performance Expectations: HS-PS Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms. The content and activity in this topic will work towards building an understanding of the structure of atoms and how elements are organized on the periodic table.
Chemical Structures The properties of elements and compounds are determined by their structures. Electrostatic Forces Electrostatic forces hold atoms in molecules.
Determine how charged matter interacts. Properties of metals and nonmetals Metals Nonmetals Physical Properties Good conductor of heat and electricity Poor conductor of heat and electricity Malleable - can be beaten or deformed without cracking; pliable Brittle Ductile - can be made into wire Non-ductile Lustrous Not lustrous, may be opaque or transparent Solid at room temperature except Hg and a few other metals that are liquid at or near room temperature Solid, liquid, or gas at room temperature Chemical Properties Usually have valence electrons Usually have valence electrons Tend to lose valence electrons Tend to gain electrons.
Other Organizational Features of the Periodic Table There are other organizational features of the periodic table. Further Investigations. Table of Contents: Atoms, Molecules, and Compounds. Activity: Electrostatic Forces. Special Features:. Representative Image:. Further Investigations: What is an Invertebrate? Question Set: What is a Mammal?
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Atomic Number. Atomic Symbol. Number of Protons. Number of Electrons. Number of Neutrons. Atoms, Molecules, and Ions. Search for:. Learning Objective Recognize the general properties of molecules. Key Points Molecules are neutral and do not carry any charge. A molecule may consist of nonmetallic atoms of a single chemical element, as with oxygen O 2 , or of different elements, as with water H 2 O.
The geometry and composition of a molecule will determine its chemical and physical properties. Show Sources Boundless vets and curates high-quality, openly licensed content from around the Internet. Licenses and Attributions. For example, sodium only has one electron in its outermost shell. It takes less energy for sodium to donate that one electron than it does to accept seven more electrons to fill the outer shell.
It is now called a sodium ion. The chlorine atom has seven electrons in its outer shell. Again, it is more energy-efficient for chlorine to gain one electron than to lose seven. Therefore, it tends to gain an electron to create an ion with 17 protons and 18 electrons, giving it a net negative —1 charge.
It is now called a chloride ion. This movement of electrons from one element to another is referred to as electron transfer. As Figure 4 illustrates, a sodium atom Na only has one electron in its outermost shell, whereas a chlorine atom Cl has seven electrons in its outermost shell. A sodium atom will donate its one electron to empty its shell, and a chlorine atom will accept that electron to fill its shell, becoming chloride.
Both ions now satisfy the octet rule and have complete outermost shells. There are four types of bonds or interactions: ionic, covalent, hydrogen bonds, and van der Waals interactions. Ionic and covalent bonds are strong interactions that require a larger energy input to break apart. When an element donates an electron from its outer shell, as in the sodium atom example above, a positive ion is formed.
The element accepting the electron is now negatively charged. Because positive and negative charges attract, these ions stay together and form an ionic bond, or a bond between ions. The elements bond together with the electron from one element staying predominantly with the other element.
Another type of strong chemical bond between two or more atoms is a covalent bond. These bonds form when an electron is shared between two elements and are the strongest and most common form of chemical bond in living organisms. Covalent bonds form between the elements that make up the biological molecules in our cells. Unlike ionic bonds, covalent bonds do not dissociate in water. The hydrogen and oxygen atoms that combine to form water molecules are bound together by covalent bonds. The electron from the hydrogen atom divides its time between the outer shell of the hydrogen atom and the incomplete outer shell of the oxygen atom.
This sharing is a lower energy state for all of the atoms involved than if they existed without their outer shells filled. There are two types of covalent bonds: polar and nonpolar. Nonpolar covalent bonds form between two atoms of the same element or between different elements that share the electrons equally. For example, an oxygen atom can bond with another oxygen atom to fill their outer shells.
This association is nonpolar because the electrons will be equally distributed between each oxygen atom. Two covalent bonds form between the two oxygen atoms because oxygen requires two shared electrons to fill its outermost shell. Nitrogen atoms will form three covalent bonds also called triple covalent between two atoms of nitrogen because each nitrogen atom needs three electrons to fill its outermost shell.
Another example of a nonpolar covalent bond is found in the methane CH 4 molecule. The carbon atom has four electrons in its outermost shell and needs four more to fill it. It gets these four from four hydrogen atoms, each atom providing one. These elements all share the electrons equally, creating four nonpolar covalent bonds Figure 5. In a polar covalent bond, the electrons shared by the atoms spend more time closer to one nucleus than to the other nucleus.
The covalent bonds between hydrogen and oxygen atoms in water are polar covalent bonds. The shared electrons spend more time near the oxygen nucleus, giving it a small negative charge, than they spend near the hydrogen nuclei, giving these molecules a small positive charge.
Figure 5. The water molecule left depicts a polar bond with a slightly positive charge on the hydrogen atoms and a slightly negative charge on the oxygen. Examples of nonpolar bonds include methane middle and oxygen right. Ionic and covalent bonds are strong bonds that require considerable energy to break.
However, not all bonds between elements are ionic or covalent bonds. Weaker bonds can also form. These are attractions that occur between positive and negative charges that do not require much energy to break. Two weak bonds that occur frequently are hydrogen bonds and van der Waals interactions. These bonds give rise to the unique properties of water and the unique structures of DNA and proteins.
Figure 6. When polar covalent bonds containing a hydrogen atom form, the hydrogen atom in that bond has a slightly positive charge. This is because the shared electron is pulled more strongly toward the other element and away from the hydrogen nucleus. This interaction is called a hydrogen bond. This type of bond is common; for example, the liquid nature of water is caused by the hydrogen bonds between water molecules Figure 6.
Hydrogen bonds give water the unique properties that sustain life. If it were not for hydrogen bonding, water would be a gas rather than a liquid at room temperature. Hydrogen bonds can form between different molecules and they do not always have to include a water molecule.
Hydrogen atoms in polar bonds within any molecule can form bonds with other adjacent molecules. For example, hydrogen bonds hold together two long strands of DNA to give the DNA molecule its characteristic double-stranded structure. Hydrogen bonds are also responsible for some of the three-dimensional structure of proteins.
Like hydrogen bonds, van der Waals interactions are weak attractions or interactions between molecules. They occur between polar, covalently bound, atoms in different molecules. Some of these weak attractions are caused by temporary partial charges formed when electrons move around a nucleus.
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