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

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

atom An atom has a positively charged center surrounded by a negatively charged area – Protons Neutrons Electrons Mass number = e – Nucleus Electron cloud

1. nucleus (positiive region) protons (positive) and neutrons (neutral) 2. electron clouds (negative region) electrons (negative) + + –– + – Protons Neutrons Electrons Mass number = e – Electron cloud 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 Elements

ELEMENTS ELEMENTS, 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 25 b.About 90 c.Over 1000

Elements Atoms and Elements periods Horizontal rows are called periods. groups Vertical columns are called groups.

Differences in Elements – Atoms of each element protons Are distinguished by a specific number of protons

IRON Atomic number Symbol Atomic mass

IRON Atomic number Atomic Mass Protons Neutrons Electrons

– Carbonhydrogenoxygennitrogen – Carbon, hydrogen, oxygen, and nitrogen 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 Sulfur b.Hydrogen, Carbon, Nitrogen and Calcium c.Carbon, Oxygen, Nitrogen and Hydrogen

What’s makes gold gold and lead lead? a.The number of protons b.The number of neutrons c.The number of electron

Isotopes Isotopes – 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 chemical bonds Form chemical bonds

Why do atoms form bonds to make molecules? a.To gather more protons for their nuclei b.To increase the number of their electrons c.To have a stable number of electrons in their outermost shell

compounds Elements can combine to form compounds – Chemical elements Combine in fixed ratios to form compounds Millions of different molecules possible Sodium Chlorine Sodium Chloride

element compound Pure substance can be found in nature Pure substance formed when two or more different elements combine. atom molecule MATTER

molecules O H H _ + +

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 Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) Na Cl Na + – – –

– An electrical attraction between ions with opposite charges Results in an ionic bond Transfer of electron Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) Na Cl Na + – – –

– 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 covalent bonds Oxygen atom (O)Carbon atom (C)Oxygen atom (O) Carbon dioxide (CO 2 )

Molecules can be represented in many ways

polar molecules Unequal electron sharing creates polar molecules – A molecule is nonpolar When its covalently bonded atoms share electrons equally (–) (+) O H H

– In a polar covalent bond Electrons are shared unequally between atoms, creating a polar molecule (–) (+) O H H Figure 2.9

Hydrogen bonds Hydrogen 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 H H

– This attraction forms weak bonds Called hydrogen bonds Hydrogen bond (+) H H (–) O

1. What type of bond is formed by sharing electrons? a.Hydrogen b.Covalent c.Ionic

2. What type of bond is very weak but important to holding together DNA? a.Hydrogen b.Covalent c.Ionic

3. What type of strong bond does salt make from sodium and chlorine? a.Hydrogen b.Covalent c.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.Covalent b.Hydrogen c.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.Covalent b.Ionic c.Hydrogen