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The Nature of Matter. Chapter 2. Atoms. Smallest particle of an element Structure of the atom Nucleus: Protons (+) Neutrons (no charge) Orbital cloud: Electrons (-) Move rapidly can be gained or lost Outer levels have a higher energy. Atoms. Duet rule:

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The Nature of Matter

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The Nature of Matter

Chapter 2


Atoms

  • Smallest particle of an element

  • Structure of the atom

    • Nucleus:

      • Protons (+)

      • Neutrons (no charge)

    • Orbital cloud:

      • Electrons (-)

        • Move rapidly can be gained or lost

        • Outer levels have a higher energy


Atoms

  • Duet rule:

    • the closest orbital around the nucleus can hold 2 electrons

  • Octet rule:

    • the cloud orbitals can hold up to 8 electrons

    • This causes attraction between atoms


Atoms

  • Neon atom

    • 10 protons

    • 10 neutron

    • 10 electrons

  • Duet Rule

  • Octet Rule

  • Stable element


Atoms

  • Charge of the atom

    • Sum of protons and electrons

    • If number of protons = number of electrons  noelectricalcharge


Atoms

  • Ion: charged particle  lose or gainelectron

    • Cl-

      • (gained 1 electron)

    • Na+

      • (lost 1 electron)

    • Ca2+

      • (lost 2 electrons)


Elements

  • Element

    • Substance that cannot be chemically broken down further

    • Consists of entirely one atom


Elements

  • Mass of the atom

    • Sum of protons and neutrons

  • Atomic #

    • Number of protons


Isotopes

  • Isotopes

    • Amount of protons ≠ number of neutrons

    • Can be more or less

    • Atomic mass is average masses of element’s isotopes


Isotopes

  • Radioactive isotopes

    • Unstable nucleus and break down at a known rate over time

    • Give off radiation which may be dangerous

    • Many uses in science

      • Tracers to follow movement within organisms

      • Ex: Carbon-14 can be used to detect the age of ancient bones


Chemical Compounds

  • Compound

    • Substance that can be broken down to elements (2 or more elements)

    • 97% of all compounds contain only 6 elements

    • C-H-O-N-P-S

    • C-H-O-N = 64%


Chemical Bonds

  • Atoms in compounds are held together by various types of bonding

  • Which part of the atom is involved in bond formation?

  • Bonds form by using valenceelectrons

  • What types of bonds are there?

    • Ionic and covalent


Ionic Bond

  • Ionic bond

    • Electrons are transferred

    • Attraction between oppositely charged ions

    • Ex: Na transfers e- to Cl  Na+Cl-

    • Become charged particles by gaining or losing electrons


Covalent Bonds

  • Covalent bond

    • Pairs of electrons in outer shell shared by both atoms

    • Can be single (2 electrons) or double (4 electrons)


States of Matter

  • Solid

    • Maintains fixed volume and shape

    • Atoms are more likely linked to each other

  • Liquid

    • Maintains a fixed volume

    • Particles move more frequently

    • Ability to flow and change into any shape

  • Gas

    • Particles move rapidly

    • Fill volume of container occupied


Chemical Reactions

  • One or more substances is made or broken down

  • Reactants

    • On the left side of an equation

    • Starting substance(s)

  • Products

    • On the right side of an equation

    • Ending substance(s)

      CO2 + H2o  H2CO2


Activation Energy

  • Energy needed in order for a reaction to occur

  • Substances known as catalysts can lower the activation energy to make a reaction start faster

    • Living things have catalysts are called enzymes that speed up reactions


Demonstration

  • Are the pieces of paper without water more attracted to each other?

  • Why are the pieces of paper with water easier to stick together?

  • What is holding the papers together?

    • Water is a polar molecule

    • Partial negative pole and partial positive side


Polarity

An uneven distribution of charges within a molecule

In a water molecule the oxygen atom has a greater ability to attract electrons to it, which pulls the hydrogen atoms to one side


Hydrogen bonding

Due to partial positive and partial negative poles on the water molecule, other water molecules are attracted to each causing a hydrogen bond

Not as strong as covalent or ionic bonding


Hydrogen Bond

http://programs.northlandcollege.edu/biology/Biology1111/animations/hydrogenbonds.html

What are the other unique properties of water?


Cohesion: The ability for water to be attracted to itself


Cohesion – Surface Tension


Adhesion - The ability for water to be attracted to other substances


Adhesion - Capillary Action

What do you

think will happen

to the daisies?

How water moves up plants

Plant tubes (xylem) are made of cellulose which is polar

Water molecules are attracted to the sides of thin tubes of xylem


Capillary Action

How water moves up plants

Water molecules are attracted to the sides of thin tubes plant walls

This is also why water moves up a straw without you doing anything!


Activity!

Drops of water on a penny

What properties of water are shown in this experiment?


pH

pH is the concentration of hydrogen ions in a solution

It is the “potential of Hydrogen”


Strong Acid and Base

  • HCl – hydrochloric acid

    • Strong acid

    • Solution would have a HIGH concentration of H+ ions

    • H+ loses electron to Cl-

  • NaOH – sodium hydroxide

    • Strong base

    • Solution would have a HIGH concentration of OH- ions

    • Na+ loses electron to OH-


Buffers

Weak acids/bases that react with strong acids or bases to have a gradual shift in the pH scale

Ex: Milk calming stomach acid


Why is water neutral?

  • The molecule of H2O separates into H3O and OH-

    • H+ loses electron to OH-

    • Equal parts of each ion

    • H2O has a neutral pH of 7


pH scale


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