Pima Medical Institute Online Education Chemical Bonds and Formulas Chemical Bonds Pima Medical Institute Online Education

Chemical Bonds ̶ ̶ ̶ The chemical behavior of atoms results from interactions among their electrons ̶ ̶ Lose, gain or share electrons 1st shell: 2 2nd shell: 8 3rd shell: 8 The chemical behavior of atoms results from interactions among their electrons. When atoms form chemical bonds they gain, lose, or share electrons. The electrons of an atom occupy one or more areas of space, called shells, around the nucleus. The maximum number of electrons that each of the first three inner shells can hold is as follows: First shell (which is closest to the nucleus): 2 electrons Second shell: 8 electrons Third shell: 8 electrons

Electron Shells IONS: Atoms that gain or lose electrons and become electrically charged The electrons in the outermost shell determine its chemical behavior Two electrons first fill its 1st shell and one electron is in the 2nd shell The single electron is located in its 1st shell Atoms whose outermost shell is filled have stable stuctures Two electrons fill its 1st shell Lose, gain or share electrons to achieve stable structures Electrons orbit the atomic nucleus. The single electron of a hydrogen atom is located in its first shell. The two electrons of a helium atom fill its first shell. Two of the three electrons of a lithium atom are in the first shell, and one is in the second shell. The electrons in the outermost shell of an atom determine its chemical behavior. Atoms such as helium, whose outermost electron shells are filled, have stable structures and are chemically inactive, or inert. Atoms such as hydrogen or lithium, whose outmost electron shells are incompletely filled, tend to gain, lose, or share electrons in ways that empty of fill their outer shells enabling them to achieve stable structures. Atoms that gain or lose electrons becomes electrically charged and are called ions.

Losing Electrons ̶ ̶ ̶ Sodium (Na) Atom 11p+ 12n0 Net electrical charge of 1+ Called a sodium ion (Na+) Sodium (Na) Atom ̶ ̶ ̶ 11p+ 12n0 An atom of sodium, for example, has eleven electrons: two in the first shell, eight in the second shell, and one in the third shell. This sodium atom tends to lose the electron from its outer shell, which leaves the second (now the outer-most) shell filled and the new form stable. Sodium is left with eleven protons (11+) in its nucleus and only ten electrons (10-). As a result, the atom develops a net electrical charge of 1+ and is called a sodium ion, symbolized by Na+ . Now this atom is stable

Gaining Electrons ̶ ̶ ̶ ̶ Chlorine (Cl) Atom 17p+ 18n0 Net electrical charge of 1- Called a chloride ion (Cl-) ̶ Chlorine (Cl) Atom ̶ ̶ 17p+ 18n0 A chlorine atom has seventeen electrons, with two in the first shell, eight in the second shell, and seven in the third shell. An atom of this type tends to accept a single electron, filling its outer shell and achieving stability. In the process, the chlorine atom is left with seventeen protons (17+) in its nucleus and eighteen electrons (18-). The atom develops a net electrical charge of 1_ and is called a chloride ion, symbolized Cl - . ̶ Now this atom is stable

Ionic (Electrovalent) Bond An ionic bond is formed when atoms gain or lose electrons Ionic bond An ionic bond (electrovalent bond) is formed when atoms gain or lose electrons. Because oppositely-charged ions attract, sodium and chloride ions react to form a type of chemical bond call an ionic bond. Sodium ions (Na+) and chloride ions (Cl-) united in this manner form the compound sodium chloride (NaCl), or table salt.

Covalent Bond A covalent bond is formed when atoms share electrons A hydrogen atom has 1 electron in its 1st shell Shared electrons Atoms may also bond by sharing electron, rather than by exchanging them. The chemical bond between the atoms that share electrons is called a covalent bond.   A hydrogen atom, for example, has one electron in its first shell but requires two electrons to achieve a stable structure. It may fill this shell by combining with another hydrogen atom in such a way that the two atoms share a pair of electrons. The two electrons then encircle the nuclei of both atoms, and each atom achieves a stable form. If one pair of electrons is shared, the resulting bond is called a single covalent bond; if two pairs of electrons are shared, the bond is called a double covalent bond. Triple covalent bonds are also possible between some atoms. Single covalent bond: 1 pair of electrons is shared Double covalent bond: 2 pairs of electrons are shared

Different types of chemical bonds share electrons to different degrees Polar Covalent Bonds Different types of chemical bonds share electrons to different degrees This atom has more than its share of electrons (slightly negative) Polar Covalent Bond When electrons are not shared equally Different types of chemical bonds share electrons to different degrees. At one extreme is the ionic bond in which atoms gain or lose electrons. At the other extreme is the covalent bond in which the electrons are shared equally. When electrons are not shared equally, a molecule whose shape gives an uneven distribution of charges results. Such a molecule is called polar. Water is an important polar molecule. Unlike an ion, a polar molecule has an equal number of protons and electrons, but one end of the molecule has more than its share of electrons, becoming slightly negative, while the other end of the molecule has less than its share, becoming slightly positive. Ionic Bond Covalent Bond

HydrogenBonds H O N A hydrogen bond is formed between an electropositive atom and an electronegative atom H O N A hydrogen bond is a chemical bond formed between an electropositive atom (typically hydrogen) and a strongly electronegative atom, such as oxygen or nitrogen. Hydrogen bonds are responsible for the bonding of water molecules in liquid and solid states, and are weaker than covalent and ionic bonds. Types of hydrogen bonds

Formulas H O O H H MOLECULAR FORMULA STRUCTURAL FORMULA H2 H2O O2 H2O (recipe) STRUCTURAL FORMULA (blueprint) H2 H H2O O O2 O H2O H H Single bond A molecular formula (recipe) consists of the symbols of the elements in the molecule together with numbers to indicate how many atoms of each element are present. For example, the molecular formula for water is H2O, which means that each water molecule consists of two atoms of hydrogen and one atom of oxygen. The molecular formula for the sugar glucose indicates that each glucose molecule consists of six atoms of carbon, twelve atoms of hydrogen, and six atoms of oxygen. A structural formula (blueprint) is drawn to represent how atoms are joined and arranged in various molecules. Single lines represent single bonds, and double lines represent double bonds. Triple covalent bonds are also possible between some atoms. Double bond C6H12O6 www.3dchem.com

3-D molecular models Three-dimensional models of structural formulas use different colors to represent the different kinds of atoms. Three-dimensional molecular models depict spatial relationships of the constituent atoms.

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