I have problem :

I want send one mail to one person using this code (for each user mail others mailadresses must be invisible , not bcc ):

global class mailSendBatchJob implements Database.Batchable<sObject>,Schedulable {
public List<String> usr{get;set;} //
public List<sObject> usr_email{get;set;}
public Map<string,string> Map_usr{get;set;}

global mailSendBatchJob(){
}

global Database.QueryLocator start(Database.BatchableContext BC){
return Database.getQueryLocator([select id,E_mail__c from invoice_statement__c where Status__c = 'Negocjowana']);
}

global void execute(Database.BatchableContext BC,List<sObject> scope){
usr = new List<String>();
usr_email = new List<sObject>();
usr.clear();
usr_email.clear();
usr_email=[select id,E_mail__c from invoice_statement__c where Status__c = 'Negocjowana'];

Map_usr=new Map<string,string>();
Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
String[] toAddresses = new String[] {};

for(sobject s : scope) {
toAddresses.add(string.valueof( s.get('E_mail__c')));
}

mail.setToAddresses(toAddresses);
mail.setSubject('Twoja faktura jest otwarta');
mail.setPlainTextBody('Twoja faktura jest otwarta');

Messaging.sendEmail(new Messaging.Singleemailmessage[] { mail });
}

global void execute (SchedulableContext sc){
MailSendBatchJob b = new MailSendBatchJob();
Database.executeBatch(b,10);
}

global void finish(Database.BatchableContext BC){
}
}

Can somebody help