What’s the MATTER? Anything that has mass and takes up space What about air ….

What’s the MATTER?

Anything that has mass and takes up space

What about air ….

Slice and Slice and dice it to dice it to as small as small a piece a piece you can you can make make it……..it……..

atom

An atomatom has a positively charged center surrounded by a negatively charged area.

+ -

+

–

6

6

6

Protons

Neutrons

Electrons

Massnumber = 12

+ +

6e–

Nucleus

Electroncloud

1. nucleus (positiive region)protons (positive) and neutrons (neutral)

2. electron clouds (negative region)

electrons (negative)

+

+

– –

+

–

2

2

2

Protons

Neutrons

Electrons

Massnumber = 4

+

+

2e–

Electroncloud

Nucleus

3 subatomic particles….. 2 regions

Electrons(-)

It’s electric … no thanks..

neutrons

NEUTRAL

protons

p.p.p.p.p.pppositive

PP ….. Ewe….

Atoms and ElementsAtoms and Elements

ELEMENTSELEMENTS, ATOMS, AND MOLECULES

• Living organisms are composed of about 25 chemical elements

– About 25 different chemical elements• Are essential to life

– About 90 naturally occurring elements• Listed on the periodic table with some

unnatural ones

• How many different naturally occuring elements are there?

a. About 25b. About 90c. Over 1000

Atoms and ElementsElements• Horizontal rows are called periodsperiods.

• Vertical columns are called groupsgroups.

•Differences in Elements– Atoms of each element

• Are distinguished by a specific number of protonsprotons

IRONIRON

Atomic number

Symbol

Atomic mass

IRONIRON

Atomic number ------- 26

Atomic Mass ------ 56

Protons -------- 26

Neutrons -------- 3030

Electrons -------- 26

– CarbonCarbon, hydrogenhydrogen, oxygenoxygen, and nitrogennitrogen

• Make up the bulk of living matter

•Trace elements Trace elements are common additives to food and water

– Dietary deficiencies in trace elements• Can cause various physiological

conditions

– Trace elements Trace elements are essential to human health

• And may be added to food or water

• Which elements are the most common in living things?

a. Carbon, Helium, Chlorine and Sulfurb. Hydrogen, Carbon, Nitrogen and

Calciumc. Carbon, Oxygen, Nitrogen and

Hydrogen

• What’s makes gold gold and lead lead?

a. The number of protonsb. The number of neutronsc. The number of electron

•IsotopesIsotopes– The number of neutrons in an atom may vary

• Variant forms of an element are called isotopes

• Some isotopes are radioactive

Table 2.4

•Electron arrangement determines the chemical properties of an atom

Hydrogen (H)Atomic number = 1

Electron

Carbon (C)Atomic number = 6

Nitrogen (N)Atomic number = 7

Oxygen (O)Atomic number = 8

Outermost electron shell (can hold 8 electrons)

First electron shell (can hold 2 electrons)

– Atoms whose shells are not full • Tend to interact with other atoms

and gain, lose, or share electrons

– These interactions• Form chemical bondschemical bonds

• Why do atoms form bonds to make molecules?

a. To gather more protons for their nucleib. To increase the number of their electronsc. To have a stable number of electrons in

their outermost shell

Elements can combine to form compoundscompounds– Chemical elements

• Combine in fixed ratios to form compounds• Millions of different molecules possible

Sodium Chlorine Sodium Chloride

elementelement

compoundcompound

Pure substance can be found in nature

Pure substance formed when two or more different elements combine.

atom

molecule

MATTERMATTER

molecules

O

HH

_

++

•Ionic bonds Ionic bonds are attractions between ions of opposite charge

– When atoms gain or lose electrons• Charged atoms called ions are created

Transfer of electron

NaSodium atom

ClChlorine atom Na+

Sodium ion

Cl–

Chloride ion

Sodium chloride (NaCl)

Na Cl ClNa

+ ––

–

– An electrical attraction between ions with opposite charges

• Results in an ionic bond

Transfer of electron

NaSodium atom

ClChlorine atom Na+

Sodium ion

Cl–

Chloride ion

Sodium chloride (NaCl)

Na Cl ClNa

+ ––

–

– Sodium and chloride ions • Bond to form sodium chloride, common table

salt

Na+

Cl–

• Ionic Bonding

•Covalent bonds Covalent bonds join atoms into molecules through electron sharing

Molecules can be represented in many ways

•Unequal electron sharing creates polar moleculespolar molecules

– A molecule is nonpolar• When its covalently bonded atoms

share electrons equally

(–) (–)

(+) (+)

O

HH

– In a polar covalent bond• Electrons are shared unequally between

atoms, creating a polar molecule

(–) (–)

(+) (+)

O

HH

Figure 2.9

• Hydrogen bondsHydrogen bonds are weak bonds important in the chemistry of life

– The charged regions on water molecules

• Are attracted to the oppositely charged regions on nearby molecules

(–) (–)

(+) (+)

O

HH

– This attraction forms weak bonds • Called hydrogen bonds

Hydrogen bond(+)

(+)

H

H(+)

(+)

(–)

(–)

(–)(–)

O

• 1. What type of bond is formed by sharing electrons?

a. Hydrogenb. Covalentc. Ionic

• 2. What type of bond is very weak but important to holding together DNA?

a. Hydrogenb. Covalentc. Ionic

• 3. What type of strong bond does salt make from sodium and chlorine?

a. Hydrogenb. Covalentc. Ionic

4. Why do atoms of elements form chemical bonds with other atoms to form molecules?

a. To fill their nucleus with a stable number of protons

b. To fill the outer shell of their atoms with a stable number of electrons

c. To add to the number of neutrons in their nucleus

5. Water is a molecule formed from Oxygen and 2 Hydrogen sharing electrons. What type of bond is this?

a. Covalentb. Hydrogenc. Ionic

6. What makes each element unique is the number of protons it has in its nucleus.

True or False

7. Which type of chemical bonding is weakest?

a. Covalentb. Ionicc. Hydrogen