covalent bonds/ substances Flashcards
(non metal to non metal)
What is a molecule?
A molecule is a group of two or more atoms bonded together by covalent bonds. These atoms can be the same (e.g., O₂) or different elements (e.g., H₂O). Molecules are the smallest units of a covalent compound that still retain the chemical properties of that compound.
What is covalent bonding?
Covalent bonding occurs when two atoms share electrons in order to achieve a stable electron configuration, usually resembling the noble gases. This type of bond forms between non-metals and involves the attraction between the shared electrons and the nuclei of the atoms.
What are intramolecular forces?
Intramolecular forces are the strong forces that hold atoms together within a molecule. These forces include the covalent bonds (single, double, or triple) that hold the atoms together.
Types of Covalent Bonds (Intramolecular Forces)
Single Covalent Bond
- Definition: A single covalent bond occurs when two atoms share one pair of electrons.
Example: In H₂ (hydrogen molecule), each hydrogen atom shares one electron with another hydrogen atom:
H–H.
Double Covalent Bond
* Definition: A double covalent bond occurs when two atoms share two pairs of electrons.
Example: In O₂ (oxygen molecule), each oxygen atom shares two electrons with another oxygen atom:
O=O.
Triple Covalent Bond
* Definition: A triple covalent bond occurs when two atoms share three pairs of electrons.
Example: In N₂ (nitrogen molecule), each nitrogen atom shares three electrons with another nitrogen atom:
N≡N.
what are the characteristics of Covalent Bonds
- Strong Bonds: Covalent bonds are strong, requiring a significant amount of energy to break. This is because the atoms are tightly bonded by the attractive forces between the shared electrons and the nuclei.
- Bond Strength: The more electrons that are shared (double or triple bonds), the stronger and shorter the bond becomes. A triple bond is the strongest, followed by a double bond, and a single bond is the weakest and longest.
types of Forces
- Strong forces of attraction within the molecule – INTRAMOLECULAR FORCES
- Weak forces of attraction between the molecules – INTERMOLECULAR FORCES
What is a Lewis structure (electron dot diagram)?
A Lewis structure (or electron dot diagram) represents the arrangement of valence electrons in a molecule. It shows how atoms are bonded and the lone pairs of electrons on atoms. The diagram uses dots to represent electrons and lines to represent bonds between atoms.
How do you draw a Lewis structure?
example of the lewis sturture
h;o;h
with 2 lone pairs on the oxygen atom
What is a Structural Formula?
A structural formula is a simplified representation of the Lewis structure. It shows the bonds between atoms using lines (each line represents a pair of electrons) and does not show the lone pairs of electrons.
how to draw structure formal
example of struture formal
h-0-h
represented by lines between the atoms
Common Molecular Shapes
There are several common shapes of molecules based on the number of bonding and lone electron pairs around the central atom. These shapes include:
Linear
Bent
Pyramidal
Tetrahedral
Linear Shape
- Description: A linear shape occurs when there are two bonding pairs and no lone pairs of electrons around the central atom. The bond angle between the atoms is 180°.
- Example: Carbon dioxide (CO₂): O=C=O. The central carbon atom forms two double bonds with two oxygen atoms, creating a straight line.
Bent Shape
- Description: A bent shape occurs when there are two bonding pairs and one or more lone pairs of electrons around the central atom. The bond angle is typically less than 120° due to the repulsion from the lone pairs.
- Example: Water (H₂O): The central oxygen atom has two lone pairs and forms two single bonds with hydrogen atoms, resulting in a bent shape with a bond angle of about 104.5°.
Tetrahedral Shape
- Description: A tetrahedral shape occurs when there are four bonding pairs of electrons around the central atom, with no lone pairs. The bond angle is 109.5°.
- Example: Methane (CH₄): The central carbon atom forms four bonds with four hydrogen atoms, resulting in a tetrahedral shape.
pyramidal Shape
- Description: A pyramidal shape occurs when there are three bonding pairs and one lone pair of electrons around the central atom. The bond angle is typically around 107°, slightly less than 109.5° due to the repulsion of the lone pair.
- Example: Ammonia (NH₃): The nitrogen atom has three bonds with hydrogen atoms and one lone pair, creating a pyramidal shape.
What does it mean for a molecule to be polar or non-polar?
- A polar molecule has an unequal distribution of electron density, resulting in a dipole moment where one part of the molecule is slightly negative and the other part is slightly positive. This occurs due to differences in electronegativity between atoms.
- A non-polar molecule has an equal distribution of electron density, so there is no permanent dipole moment. This can occur if the molecule is symmetrical or the atoms involved have the same electronegativity.
What is electronegativity and how does it affect polarity?
Electronegativity is the ability of an atom to attract shared electrons in a covalent bond. When two atoms have different electronegativities, the atom with the higher electronegativity will pull the electron density towards itself, creating a partial negative charge (δ-) on that atom and a partial positive charge (δ+) on the other atom. This creates a polar bond.
Large electronegativity difference → polar bond(greater than >0.4) (e.g., H₂O).
Small or no electronegativity difference → non-polar bond (e.g., H₂).
What is the role of VSEPR theory in determining molecular polarity?
The Valence Shell Electron Pair Repulsion (VSEPR) theory helps determine the shape of the molecule, which is critical in understanding if the dipoles (polarities) within the molecule cancel out or add up.
- Symmetrical shapes (e.g., linear, tetrahedral) with identical bonds often result in a non-polar molecule, even if individual bonds are polar, because the dipoles cancel each other out.
- Asymmetrical shapes (e.g., bent, pyramidal) with polar bonds often result in a polar molecule because the dipoles do not cancel out.
How to Identify if a Molecule is Polar or Non-polar
Follow these steps:
Check the Electronegativity Difference:
- If there is a significant difference in electronegativity between atoms, the bond is likely polar.
- If the electronegativity difference is small or zero, the bond is non-polar.
- Determine the Shape of the Molecule (VSEPR Theory):
- If the molecule is symmetrical (e.g., CO₂), the dipoles cancel out, and the molecule is non-polar.
- If the molecule is asymmetrical (e.g., H₂O), the dipoles do not cancel out, and the molecule is polar.
- Check for Lone Pairs on the Central Atom:
- Molecules with lone pairs on the central atom (e.g., NH₃) are often polar because the lone pairs cause an asymmetrical distribution of electron density.
What are intermolecular forces?
Intermolecular forces are the forces of attraction or repulsion between molecules. These forces are generally weaker than intramolecular forces (like covalent or ionic bonds), but they play a crucial role in determining the physical properties of substances, such as boiling point, melting point, and solubility.
Dispersion Forces
Definition: Dispersion forces are the weakest type of intermolecular force. They arise from temporary fluctuations in the electron distribution within atoms or molecules, which create instantaneous dipoles. These dipoles induce temporary dipoles in nearby molecules, resulting in attraction.
what are the Types of Intermolecular Forces
Dispersion Forces (London Dispersion Forces)
Dipole-Dipole Forces
Hydrogen Bonds (HFON)
Dipole-Dipole Forces
Definition: Dipole-dipole forces occur between molecules that have permanent dipoles (polar molecules). These forces arise because the positive end of one molecule is attracted to the negative end of another molecule.
(require alot of energy to break)
Hydrogen Bonds (HFON)
Definition: A hydrogen bond is a stronger type of dipole-dipole interaction that occurs when a hydrogen atom is bonded to a highly electronegative atom, such as fluorine (F), oxygen (O), or nitrogen (N). These atoms have a strong attraction for the hydrogen atom, creating a very strong dipole. (they require the most energy to break)
