chemical bonds 🧪
Chemical Bonds
forces that hold atoms together in molecules
Ionic Bonds: These occur when electrons are transferred from one atom to another, resulting in the formation of positively charged ions (cations) and negatively charged ions (anions). The electrostatic attraction between these oppositely charged ions holds the bond together. Ionic bonds typically form between metals and nonmetals. An example is sodium chloride (NaCl).
Covalent Bonds: These occur when two atoms share electrons to achieve a stable electron configuration. Covalent bonds can be either nonpolar (where the electrons are shared equally) or polar (where the electrons are shared unequally due to differences in electronegativity). Covalent bonds typically form between nonmetal atoms. An example is a water molecule (Hâ‚‚O).
Metallic Bonds: These occur in metals, where electrons are not associated with any specific atom but instead flow freely throughout a lattice of metal cations. This “sea of electrons” gives metals their characteristic properties, such as conductivity and malleability. An example is the bonding in a copper wire.
sometimes atoms gain or lose electrons to maximize filling their outer levelsÂ
if an atom gains or loses electrons it will become chargedÂ
ions are charged atoms or a group of atomsÂ
cation: if an atom loses electrons it will gain a positive charge equal to the number of electrons lost
anion: if an atom gains electrons it will develop a negative charge equal to the number of electrons gainedÂ
opposite charges attract one anotherÂ
electronegativity: the ability of an atom to attract a shared pair of electronsÂ
When it comes to covalent bonds, the more electronegative atom attracts the shared pair of electrons more strongly than the less electronegative atom.
 The more electronegative atom becomes partially negatively charged, and the less electronegative atom becomes partially positively charged. For example, you can see in the table above that oxygen is a lot more electronegative than hydrogen. This is why the oxygen atom in an O-H bond becomes partially negatively charged, and the hydrogen atom becomes partially positively charged.
When it comes to covalent bonds, the more electronegative atom attracts the shared pair of electrons more strongly than the less electronegative atom.Â
The more electronegative atom becomes partially negatively charged, and the less electronegative atom becomes partially positively charged.
 This is why the oxygen atom in an O-H bond becomes partially negatively charged, and the hydrogen atom becomes partially positively charged.
Polar covalent bonds are a type of covalent bond in which the electrons are not shared equally between the two atoms involved. This occurs because the atoms have different electronegativities, which is the ability of an atom to attract electrons toward itself.
In a polar covalent bond, the more electronegative atom pulls the shared electrons closer to itself, resulting in a partial negative charge (δ-) on that atom and a partial positive charge (δ+) on the less electronegative atom. This creates a dipole, meaning the molecule has a positive end and a negative end.
A common example of a polar covalent bond is the bond between hydrogen and oxygen in a water molecule (Hâ‚‚O). Oxygen is more electronegative than hydrogen, so the electrons are drawn closer to the oxygen atom, making the oxygen side of the molecule slightly negative and the hydrogen side slightly positive.
Hydrogen bond: a weak attraction of H atoms to other atoms that are covalently bonded to something else. It is important to stabilize biological molecules, such as proteins and nucleic acidsÂ
Properties of Hâ‚‚O
water acts as dipole, has one positive end and one negative endÂ
oxygen and hydrogen share electrons but not equal electronsÂ
temperature stability: water changes temperature more slowly than air because H bonds can absorb and release energy
kinetic energy: energy of motion or vibrationÂ
temperature measures the intensity of kinetic energy an atom has
Polarity: Water is a polar molecule, meaning it has a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity allows water to dissolve many substances, making it an excellent solvent.
Hydrogen Bonding: The polar nature of water molecules leads to hydrogen bonding, where the slightly positive hydrogen atoms are attracted to the slightly negative oxygen atoms of nearby water molecules. These hydrogen bonds are responsible for many of water’s unique properties.
Cohesion: Water molecules stick to each other due to hydrogen bonding, leading to high surface tension. This is why water forms droplets and allows certain insects to walk on water.
Adhesion: Water also sticks to other polar or charged surfaces, which is important in processes like capillary action (the movement of water up a narrow tube, such as in plant roots).
High Specific Heat Capacity: Water has a high specific heat capacity, meaning it can absorb or release a significant amount of heat without a large change in temperature. This property helps regulate temperature in environments, such as stabilizing climate and maintaining body temperature in organisms.
High Heat of Vaporization: Water requires a lot of energy to change from a liquid to a gas. This is due to the strength of the hydrogen bonds that need to be broken during vaporization. This property is why sweating effectively cools the body, as water absorbs a lot of heat when it evaporates from the skin.
Solid state (Ice) is less dense than the liquid state because unlike most substances, water expands when it freezes, making ice less dense than liquid water. This is why ice floats on water.Â
This property is crucial for aquatic life because it insulates bodies of water, preventing them from freezing solid.
Water expands as a solid and changes temperature slower than air because hydrogen bonds can absorb and release energy.
High Surface Tension: Due to cohesion and hydrogen bonding, water has a high surface tension, allowing it to form droplets and resist external force to a certain extent. This property plays a key role in biological systems, such as in the alveoli of the lungs.
Universal Solvent: Water is often called the “universal solvent” because it can dissolve a wide range of substances, particularly ionic compounds and polar molecules. This makes water essential in biological systems for transporting nutrients, waste, and other substances.Â
Capillary Action: The combination of adhesion and cohesion allows water to move against gravity in narrow spaces, such as the xylem in plants, which helps in the transport of water from roots to leaves.