GROUP-2-7TH-PRESENTER_20250723_231121_0000.pptx

STRUCTURE AND POLARITY

1. STRUCTURE AND POLARITY OF A MOLECULE PHYSICAL SCIENCE : CHAPTER 3 LESSON 1 PRESENTED BY GROUP 2 (7TH PRESENTER)

2. LEARNING OBJECTIVES • Explain how polar and nonpolar bonds form • Identify the factors that influence molecular polarity • Identify the conditions that make a molecule polar of nonpolar. • Explain the principle “like dissolves like”.

3. SCIENCE PIONEER GILBERT NEWTON LEWIS was an American Chemist and Dean of the College of Chemistry at the University of California, Berkeley, during the first half of the twentieth century until he died in 1946. He also served as the Superintendent of the Bureau of Weights and Measures in Manila, Philippines from 1904 to 1905. He proposed the “cubic atom arrangement” of electrons around the nucleus, wherein each valence electron occupies a spot at each corner of an imaginary cube enclosing the atom.

4. A REVIEW OF THE BASIC CONCEPTS Everything is made of tiny particles called atoms. Atoms connect to each other through two main types of bonds: ionic bonds (electrons are transferred) and covalent bonds (electrons are shared). The way atoms bond determines what kind of substance is formed.

5. Molecular Shape and Polarity A molecule's shape and how its atoms are arranged (its structure) determine its physical and chemical properties. Molecular formulas and Lewis structures help us visualize and understand these arrangements.

6. Molecular Shape and Polarity Lewis structures show how atoms are bonded in a molecule. They show the relative location of atoms and the number of covalent bonds present. The dots represent bonding pairs of valence electrons.

7. The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular shape. Electron groups (bonding pairs and lone pairs) around a central atom repel each other, arranging themselves to minimize repulsion. This arrangement dictates the molecule's overall shape. Single, double, and triple bonds all count as one electron group.

8. Molecular shapes are classified using a specific (ABxNy) designation. 'A' represents the central atom, 'B' represents the number of bonding electron groups, and 'N' represents the number of nonbonding electron groups, and 'X' and 'Y' are integers that pertain to the number of bonding or nonbinding electron groups.

9. By convention, a solid line ( — ) represents a bond that lies on the plane of the paper. A dashed wedge line stands for a bond behind this plane and away from the viewer. A solid wedge line indicates a bond that protrudes from the paper toward the viewer.

10. VSEPR theory established that electron groups, separated by well-defined angles, agree with experimental measurements on real molecules. Experimental measurements on molecules like CH₄ and PCl₅ confirm bond angles predicted by the theory.

11. Lone pairs push harder than bonding pairs, making bond angles smaller and changing the shape of molecules. For example, NH₃ has one lone pair, so its bond angle is 107.3° instead of 109.5°. Water has two lone pairs, making the angle even smaller.

12. Molecular Shape and Polarity Molecular shape helps determine if a molecule is polar. In molecules like HCl, electrons are shared unevenly because chlorine pulls more electrons than hydrogen. This makes chlorine slightly negative and hydrogen slightly positive. The bigger the difference in how strongly atoms pull electrons (electronegativity), the more polar the bond is.

13. Molecular Shape and Polarity Another way to represent a dipole is to draw an arrow or a vector pointing in the direction of more electromagnetic atom while making the tail of the arrow a plus or a cross sign to emphasize a partial positive charge on that end.

14. A molecule is said to be polar if : • polar bonds are present, and they are arranged in such a way that the bond dipoles do not cancel, or • nonpolar bonds and lone pairs on the central atom are present, and they are arranged in such way that they do not cancel each other.

15. 01 In contrast, a molecule is said to be nonpolar if there are no polar bonds or lone pairs in the central atom. And if there are polar bonds or lone pairs, they are arranged in such a way that their polarities cancel one another.

16. 02 Carbon dioxide (CO2) has a linear molecular shape, has two polar bonds (C=O), and has no lone pair in it's central atom; yet it is a nonpolar molecule since it's bonds are arranged in a way that dipoles cancel each other. A water molecule, having a bent shape, polar H—O bonds, and two lone pairs that do not cancel each other, is polar.

17. Polar molecules are soluble in water, while nonpolar molecules are not. In terms of the similarity of the overall polarity of the substances being mixed, the general principle “like dissolves like” holds. In other words, polar substances dissolve polar substances; nonpolar substances dissolve nonpolar substances “LIKE DISSOLVES LIKE”

18. Thank you! Do you have any questions? GOD BLESS!