Polarity Of Molecules - PhySci Week 3 Lesson

POLARITY OF MOLECULES This presentation will guide you through the fascinating world of chemical bonds, focusing on the concept of polarity and its impact on molecular properties. Karl Louise F. Ibarrientos SST-I  BOND POLARITY AND ELECTONEGATIVITY DAY 1 KEY CONCEPTS:...

POLARITY OF MOLECULES This presentation will guide you through the fascinating world of chemical bonds, focusing on the concept of polarity and its impact on molecular properties. Karl Louise F. Ibarrientos SST-I  BOND POLARITY AND ELECTONEGATIVITY DAY 1 KEY CONCEPTS: A Covalent Bond is formed by the equal sharing of electrons from both participating atoms. The pair of electrons participating in this type of bonding is called a shared pair or bonding pair. Covalent bonds are also called KEY CONCEPTS: Polarity refers to uneven distribution of electrical charge within a molecule. This creates a regions with slightly positive and slightly negative charges. Factors determining Polarity: ELECTRONEGATIVITY is the ability of an atom to attract electrons toward itself in a chemical bond. increases from left  The electronegativity to right of a period and decreases from top to bottom of a group. The higher the value of EN, the element tends to attract electron towards itself.  When two atoms with different electronegativities bond, the electrons are not shared equally. The more electronegative atom pulls the electrons closer, creating a partial negative charge on itself and a partial positive charge on the less ACTIVITY 1.1: Determine if it is POLAR or NONPOLAR Note: Use a Pauling electronegativity values then look at Table 1 for EN differences H-H, C-O  Polar Bond: If two atoms with different electronegativities form a bond, the electron density will be pulled closer to the more electronegative atom, creating partial positive (δ⁺) and partial negative (δ⁻) charges. Nonpolar Bond: If atoms have the same or similar electronegativities, they share electrons equally, resulting in no partial charges. Key Concept: Electronegativity differences dictate the polar nature of a bond. A polar covalent bond is formed when electrons are shared unequally by two atoms in a compound. The bonded pair of atoms form an electric dipole (represented by ). Dipole means “two poles” which means that a molecule has one positive end and one negative end. In this type of bond, the atom with the higher EN value becomes the partial negative pole (symbolized as ẟ - ) while the atom with the lower EN value becomes the partially positive (symbolized as ẟ +) pole. Always bear in mind that the direction of the arrow is always pointing from a more electropositive pole to the more electronegative pole. Take HCl for example, H has higher EN than Cl, thus the direction of the arrow is pointing away from H and towards Cl. There is unequal electron MOLECULAR GEOMETRY DAY 2-3 Factors determining Polarity: MOLECULAR GEOMETRY Even if a molecule has polar bonds, the overall molecule might be nonpolar if the geometry of the molecule causes Factors determining Polarity: MOLECULAR GEOMETRY For example in Carbon Dioxide (CO2), the two polar bonds between carbon and oxygen are oppositely directed, KEY CONCEPT VSEPR Theory is a model used to predict the shape (geometry) of a molecule based on the repulsion between electron pairs in the valence shell of the central atom. According to VSEPR theory, electron pairs (bonding and lone pairs) around a central atom will arrange themselves in a way that minimizes repulsion, leading to a specific molecular shape. KEY POINT Electron pairs: Both bonding pairs (shared electrons in a bond) and lone pairs (non-bonding electrons) exert repulsive forces. Electron pair repulsion: The more electron pairs around the central atom, the greater the repulsion, which influences the shape of the molecule. Predict the shape or molecular geometry of a substance using the following steps: Step 1: Determine the central atom of a molecule. The central atom is the least electronegative element. Step 2: Draw the appropriate Lewis dot structure for the molecule. Step 3: Count the number of bonding pairs of electrons and non-bonding (or lone pairs) around the central atom. Step 4: Determine the electron pair orientation  In polyatomic molecules (i.e., molecules made up of three or more atoms), one of the constituent atoms is identified as the central atom to which all other atoms belonging to the molecule are linked. The total number of valence shell electron pairs decides the shape of the molecule. The electron pairs have a tendency to orient themselves in a way that minimises the electron-electron repulsion between them and maximises the distance between them. The valence shell can be thought of as a sphere wherein the electron pairs are localised on the surface in such a way that the distance between them is maximised. Should the central atom of the molecule be surrounded by bond pairs of electrons, then the asymmetrically shaped molecule can be expected. Should the central atom be surrounded by both lone pairs and bond pairs of electrons, the molecule would tend to have a distorted shape. The VSEPR theory can be applied to each resonance structure of a molecule. The strength of the repulsion is strongest in two lone pairs and weakest Activity 2.1 Molecular Shape Exploration: Introduce VSEPR theory and explain how electron pairs arrange themselves to minimize repulsion, leading to specific molecular shapes. oStudents will draw molecules such as CH₄ (tetrahedral), H₂O (bent), and CO₂ (linear). oAs you draw the molecules, you will identify whether the molecule is polar or nonpolar by considering both bond polarity and the symmetry of the molecule. KEYPOINT oEven if a molecule contains polar bonds, its geometry may cause the molecule to be nonpolar. Symmetrical molecules (e.g., CO₂) can cancel out dipole moments, making the molecule nonpolar. oKey Concept: The overall molecular polarity depends on the combination of bond polarity and the shape of the molecule. ssignment: Home Activity THANK YOU!!!