Flashcards in Lecture 7 Deck (21)
What is an ionic bond?
An ionic bond is formed when one atom accepts or donates one or more of its valence electrons to another atom
If the electronegativity values of two atoms are different, ionic bonds are formed
Most salts are ionic and dissolve in water
The ionic compound or salt conducts electricity when dissolved in water
Ionic bond compounds are electrolytes
What are anions and cations?
Requires one positive ion (cation) and one negative ion (anion)
If a neutral atom gains one or more electrons it becomes an anion
Metal (cation) + Nonmetal (anion) = ionic bond
What is a covalent bond?
Covalent bonds occur when two or more nonmetal atoms come together and share valence electrons to become stable
Each atom donating half of the electrons to be shared (equal sharing)
Covalent bonds are strong, they do not break when in water
Compounds containing covalent bonds are nonelectrolytes
Covalent molecules have lower melting and boiling points than ionic compounds
What are bonding and nonbonding electrons?
The electrons involved are called bonding electrons
The electrons not involved are called non- bonding electrons
What is a Single Covalent Bond ?
Both atoms donate one electron
One pair of electron is shared between atoms
Bond can be represented by a single line or dash
H-H → Hydrogen gas (H2)
or cl-cl Chlorine gas or HCL
What is a double Covalent Bond ?
A double covalent bond is two pairs of electrons (4) being shared
Bond is represented by a double line
like Oxygen gas
Ethylene, C2H4 , C=C
What is a triple Covalent Bond ?
A triple covalent bond is the sharing of three pairs of electrons (6)
What does polarity depend on ?
Polarity depends on the electronegativity of the atoms involved
Electronegativity – attraction of an atom for electrons in a covalent bond
Nonpolar and polar covalent bonds
Dependent on the charge at the ends of the molecule
What is electronegativity?
The attraction or affinity of an atom for electrons in a chemical bond (covalent)
Elements with high electronegativity attract electrons more easily\
Elements with low electronegativity have a lesser tendency to attract electrons
What is a non polar covalent bond?
Two atoms with the same electronegativity will share the bonding electron pairs equally
No separation of charges
H-H or H:H pure covalent bond or O-O
same atom), same electronegativity, same charge at both ends of the molecule
What is a polar covalent bond?
If two bonded atoms have different electronegativity, the bonding pairs of electrons will be shared unequally
They are different atoms, difference in electronegativity, different charge at both ends of the molecule
Represented by S+ and S-
Like H (S+) and Cl (S-)
The single bond between a Hydrogen and a Chloride as in H-Cl will have the bonding pair closer to the higher electronegative atom (Chloride)
What are some basic rules?
Non metals are more electronegativity than metals
Metals lose electrons more easily
Most covalent bonds involve atoms of non- metallic elements
What are hydrogen bonds?
The interaction between the hydrogen attached to an electronegative atom of one molecule, with an electronegative atom of a different molecule
Usually nitrogen, oxygen or fluorine
The Hydrogen bond is weaker than covalent or ionic bonds
Occur in both inorganic molecules such as water and organic molecules such as DNA
What is a chemical indicator?
Chemical indicator, any substance that gives a visible sign, usually by a colour change, of the presence or absence of a threshold concentration of a chemical, such as an acid or an alkali in a solution
Must be both sensitive and easily detectable
Doesn't change the conditions of the sample
What is an acid base indicator?
An acid-base indicator is either a weak acid or weak base that exhibits a color change as the concentration of hydrogen (H+) or hydroxide (OH-) ions changes in an aqueous solution
Used in titration to identify the endpoint of an acid-base reaction
Used to gauge pH values
Litmus paper and pH paper are used for quick, relatively imprecise measurements
What is pH
pH is a logarithmic measure of the hydrogen ion concentration of an aqueous solution:
pH = -log[H+]
Where log is the base 10 logarithm and [H+] is the hydrogen ion concentration in moles per liter
Very strong acids may have a negative pH
Very strong bases may have a pH exceeding 14
What is pH indicator?
A pH indicator change color over a narrow range of pH values in solution
pH indicators display different colors between certain pH limits
Blue litmus paper turns red in acidic conditions, and red litmus paper turns blue under basic conditions
What is pH of blood
7.35 and 7.45
The glomerular filtrate of blood is usually acidified by the kidneys from a pH of approximately 7.4 to a pH of about 6 in the urine
What is pH of urine?
4.5 to 8
What are the parts of a pH meter?
pH meter involves a pH-sensitive electrode (measuring electrode) is based on H ion activity
The reference electrode provides a constant voltage for comparison
The difference between the two voltages is displayed as a pH value by the meter
Higher voltages signals - acidic pH levels and lower voltages signals - basic