Shape Of Molecules Flashcards
What is the result of substances being attracted by a non-uniform electrostatic field?
“They are said to be polar. “
What is the result of substances not being deflected by a non-uniform electrostatic field?
“They are said to be non-polar. “
Give examples of polar liquids.
“Trichloromethane and Ethanol. “
Give examples of non-polar liquids.
“Tetrachloromethane
What is a polar molecule?
“One that contains positive and negative poles. “
What kind of charges are in a polar molecule?
“A partial positive charge (δ+) at one point and a partial negative charge (δ-) at another point. “
Why are bonding electrons in a hydrogen chloride molecule not shared equally?
“Because the chlorine has a greater attraction for the electrons than the hydrogen atom. “
What is another term for the electron attracting power of an atom?
“Electronegativity. “
What is polarization?
“The overall distortion of charge in molecules resulting from the unequal sharing of electrons. “
What is a dipole?
“The separation of charges in a molecule. “
How is the uneven distribution of electrons in hydrogen chloride represented?
“As an electron cloud. “
What kind of dipole results from the centers of positive and negative charge not coinciding?
“A permanent electric dipole. “
How is an electric dipole conventionally represented?
“By an arrow pointing towards the negative end. “
What happens when polar liquids flow from a burette past a positively charged rod?
“The negative ends of the polar molecules are attracted towards the rod. “
What happens when polar liquids flow from a burette past a negatively charged rod?
“The positive ends of the polar molecules are attracted towards the rod. “
Which is deflected by a non-uniform electrostatic field: trichloromethane or tetrachloromethane?
“Trichloromethane. “
What kind of distribution of atoms does tetrachloromethane have?
“A symmetrical distribution. “
What is each of the four bonds in tetrachloromethane?
“A dipole
Why is tetrachloromethane non-polar?
“Because the equal dipoles cancel each other. “
Is the structure of trichloromethane symmetrical?
“No. “
Why is trichloromethane polar?
“Because its dipoles do not cancel each other. “
Name three factors that determine whether a molecule is polar or non-polar.
“The polarity of the covalent bond
What shape is assumed for carbon (IV) oxide given it is non-polar?
“Linear. “
What does the polarity in molecules like hydrogen chloride and water result from?
“The presence of highly electronegative elements such as oxygen and chlorine. “
What is electronegativity according to Linus Pauling?
“The power of an atom in a molecule to attract electrons to itself. “
What is the general trend for electronegativity in the Periodic Table?
“It increases across the table and decreases down the groups. “
Which element is the most electronegative?
“Fluorine. “
Which element is the least electronegative?
“Caesium. “
What kind of bonds will form between elements of widely different electronegativities?
“Highly polar
What kind of bonds will form between elements of similar electronegativities?
“Non-polar or only slightly polar and essentially covalent if the elements are non-metals. “
What does the existence of a dipole confer to a covalent molecule?
“Partial ionic character. “
What happens to the ionic character of a substance as the polarity of the molecule increases?
“It also increases. “
What is the nature of most covalent bonds?
“They involve unequal sharing of electrons
What is the nature of many ionic compounds?
“They indicate varying degrees of covalent bonding. “
What should be realized about wholly ionic and wholly covalent bonds?
“That they are extreme types. “
What is the shape of simple covalent molecules?
“They have definite shapes. “
How do atoms combine in covalent molecules?
“By sharing electrons. “
How is a single covalent bond formed?
“From the overlap of two atomic orbitals
What is the direction of a covalent bond?
“It is oriented in the direction of the orbitals which provide electrons. “
What is the central atom in methane?
“Carbon. “
What influences the shape of a covalent molecule like methane?
“The total number of electron pairs in the valence shell of its central atom. “
What do electron pairs include?
“Shared (bonding) pairs and lone (non-bonding) pairs. “
What kind of charge do electron clouds have?
“Negative. “
How do electron clouds arrange themselves in a molecule?
“They mutually repel each other and stay as far apart as possible. “
What is the electronic configuration of carbon?
“1s²2s²2p². “
How many unpaired electrons does carbon have in its valence shell?
“Two. “
What is the valency of carbon in methane and most carbon compounds?
“Four. “
How does carbon achieve a valency of four?
“One of the 2s electrons is promoted to occupy the empty 2pz orbital
How many bond pairs of electrons does the carbon atom in methane have?
“Four. “
What is achieved when the carbon atom in methane has four bond pairs of electrons?
“The octet electronic configuration. “
Are the C-H bonds in methane identical?
“Yes. “
How can it be explained that the C-H bonds in methane are identical?
“If the 2s and three 2p orbitals merge or hybridize to form four new orbitals that are identical. “
What are the new set of four hybrid orbitals called?
“sp³. “
What shape do the four bond pairs of electrons in methane assume to minimize repulsion?
“A regular tetrahedron. “
Where does the carbon lie in the tetrahedral arrangement of methane?
“In the center. “
Where are the hydrogen atoms located in the tetrahedral arrangement of methane?
“At the apices of the tetrahedron. “
What is the bond angle between any two covalent bonds in methane?
“Approximately 109°. “
What is the central atom in ammonia?
“Nitrogen. “
What is the electronic configuration of nitrogen?
“1s²2s²2p³. “
How many unpaired electrons does nitrogen have in its 2p orbitals?
“Three. “
How many lone pairs does nitrogen have in its 2s orbital?
“One. “
How many bond pairs and lone pairs of electrons does the nitrogen atom in ammonia have?
“Three bond pairs and one lone pair. “
What rule is satisfied by the nitrogen atom in ammonia having three bond pairs and one lone pair?
“The octet rule for stability. “
What is the shape of the ammonia molecule?
“Pyramidal.”
What is the shape of the water molecule?
“Tetrahedral.”
How many bond pairs and lone pairs of electrons does the oxygen atom in water have?
“Two bond pairs and two lone pairs.”
What is the bond angle in a water molecule?
“104.5°.”
Why is the bond angle in water less than the tetrahedral angle of 109.5°?
“Because the lone pairs of electrons repel each other more than the bond pairs.”
What is the shape of carbon (IV) oxide?
“Linear.”
Why is carbon (IV) oxide linear?
“Because the two pairs of electrons are on opposite sides of the carbon atom and repel each other equally.”
What are the shapes of boron trichloride and beryllium chloride?
“Planar.”
What is the bond angle in boron trichloride?
“120°.”
What is the bond angle in beryllium chloride?
“180°.”
What is the shape of molecules with an expanded octet, like phosphorus pentachloride and sulphur hexafluoride?
“They do not have a tetrahedral shape.”
What shape does phosphorus pentachloride (PCl5) have?
“Trigonal bipyramidal.”
What shape does sulphur hexafluoride (SF6) have?
“Octahedral.”
What is the valence shell electron pair repulsion theory?
“A theory that predicts the shapes of molecules based on the repulsion of electron pairs around the central atom.”
What are the basic principles of the valence shell electron pair repulsion theory?
“Electron pairs
What is the order of repulsion strength between electron pairs?
“Lone pair - lone pair > lone pair - bond pair > bond pair - bond pair.”
What are the steps to predicting the shape of a molecule using the valence shell electron pair repulsion theory?
“1. Draw the Lewis structure. 2. Count the total number of electron pairs around the central atom. 3. Arrange the electron pairs to minimize repulsion. 4. Determine the molecular shape based on the arrangement of the bonding pairs.”
What are the five basic shapes of molecules?
“Linear
What is the bond angle in a linear molecule?
“180°.”
What is the bond angle in a trigonal planar molecule?
“120°.”
What is the bond angle in a tetrahedral molecule?
“109.5°.”
What are the bond angles in a trigonal bipyramidal molecule?
“90°
What are the bond angles in an octahedral molecule?
“90° and 180°.”
What are intermolecular forces?
“The forces of attraction between molecules.”
What are van der Waals forces?
“Weak attractive forces between molecules.”
What are the two types of van der Waals forces?
“Dipole-dipole forces and London dispersion forces.”
What are dipole-dipole forces?
“Attractive forces between polar molecules.”
What are London dispersion forces?
“Weak attractive forces that occur between all molecules
What is hydrogen bonding?
“A strong type of dipole-dipole interaction between hydrogen and a highly electronegative atom like oxygen
How does hydrogen bonding affect the physical properties of substances?
“It increases boiling points and influences solubility.”
What are the four types of solids?
“Ionic
What are the characteristics of ionic solids?
“High melting points
What are the characteristics of covalent solids?
“High melting points
What are the characteristics of metallic solids?
“Good conductivity
What are the characteristics of molecular solids?
“Low melting points and poor conductivity.”
What is a crystal lattice?
“The regular
What is the difference between crystalline and amorphous solids?
“Crystalline solids have a long-range order in their structure
What is the effect of alloying on the properties of metals?
“Alloying can prevent the sliding of layers of metallic ions
