Presentation for Bilogy-The Nature of Matter

8/3/2019 Presentation for Bilogy-The Nature of Matter

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The Nature of Matter


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Atom

The study of chemistry begins with the basic unit ofmatter, the atom. Word atom comes from Greek

wordatomos

which means indivisible. By now scientists know that atom can be divided.

The atoms are incredibly small, if we place side by

side 100 million atoms it would make a row onlyabout 1cm long.


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The subatomic particles that make up atoms areprotons, neutrons and electrons.

Protons are positively charged (+)

Neutrons have no charge.

Electrons are negatively charged. (-)


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Elements and Isotopes

A chemical element is a pure substance that consistsentirely of one type of atom.

More than 100 elements are known but only onedozen are commonly found in living organisms.

Elements are represented by a one-or-two-letter

symbol.


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Isotopes

Atoms of an elements can have different numbers ofneutrons.- Atoms of the same element that differ in the number of

neutrons they contain are know as isotopes.- The sum of the protons and neutrons in the nucleus ofan atom is called its mass number.

Isotopes are identified by their mass number.- The weighted average of the masses of an elementsisotopes is called its atomic mass.- Because they have the same number of electrons, allisotopes of an element have the same chemicalproperties.


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Isotopes of Carbon


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Radioactive Isotopes

Some isotopes are radioactive, meaning that theirnuclei are unstable and break down at a constantrate over time.

These isotopes can be dangerous, but radioactiveisotopes have a number of important scientific and

practical uses.


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Chemical Compounds

A chemical compound is a substance formed by thechemical combination of two or more elements indefinite proportions.

H2O-water

The physical and chemical properties of acompound are usually very different from those ofthe elements from which it is formed.


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Chemical Bonds

The atoms in compound are held together bychemical bonds.

Main type of chemical bonds are ionic bonds andcovalent bonds.


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Ionic bonds

An ionic bond is formed when one or moreelectrons are transferred from one atom to another.Recall that atoms are electrically neutral becausethey have equal numbers of protons and electrons.

Atom which loses electrons has a positive charge.An atom that gains electrons has a negative charge.

These positively an negatively charged atoms areknown as ions.


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Covalent Bonds

A covalent bond forms when electrons are sharedbetween atoms.

When atoms share two electrons, the bond is calleda single covalent bond. Sometimes the atoms sharefour electrons and form a double bond. In a fewcases, atoms can share six electrons and form atriple bond.

The structure that results when atoms are joinedtogether by covalent bonds is called a molecule.The molecule is the smallest unit of mostcompounds.


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Van der Waals Forces

Because of their structure atoms of differentelements dont all have the same ability toattract electrons.

When molecules are close together, a slightattraction can develop between the oppositely

charged regions of nearby molecules. Chemistcall such intermolecular forces of attraction vander Waals forces, after the scientist thatdiscovered them.


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Gecko

People who keep geckos as their pets theyalready seen van der Waals force. These lizardscan climb up smooth surfaces as glass wallsand hang on by a single toe despite the pull ofgravity.

Van der Waals forces from between moleculeson the surface of the geckos foot andmolecules on the surface of the wall.


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Presentation for Bilogy-The Nature of Matter